[PAUTHABIELF64] Remove alternative ELF marking scheme

No implementation is using the alternative marking scheme; take
the opportunity to remove it, so that toolchains do not need to
support it.

The alternative marking scheme started as the default one back
when the spec was written. At the time there were only prototype
implementations for which signing schema compatibility and
versioning weren't important.

Over time Arm's ELF marking for SysV has evolved such that the
preference for ELF executables and shared-libraries is to use
GNU Program Properties. We intend to migrate to Build Attributes
for relocatable objects, but until that change is made GNU
Program Properties should be used in relocatable objects too.

The alternative ELF marking scheme was preserved for backwards
compatibility, however no current implementation needs that so
it can be removed.

pauthabielf64/pauthabielf64.rst

@@ -236,7 +236,9 @@ changes to the content of the document for that release.
   |            |                             | DT_AARCH64_VARIANT_PCS.                                          |
   +------------+-----------------------------+------------------------------------------------------------------+
   | 2024Q1     | 29\ :sup:`th` January 2024  | Update preferred ELF marking scheme to be GNU property based     |
-  | 2023Q4     | 18\ :sup:`th` March 2024    | Update relocation codes to move out of private experiments space.|
+  |            | 18\ :sup:`th` March 2024    | Update relocation codes to move out of private experiments space.|
+  |            | 19\ :sup:`th` March 2024    | Remove alternative ELF marking scheme. No implementation is      |
+  |            |                             | using it.                                                        |
   +------------+-----------------------------+------------------------------------------------------------------+
 
 References
@@ -852,13 +854,6 @@ This document defines the core information that any ELF marking
 scheme must contain and the base compatibility model that uses that
 information.
 
-The default ELF marking scheme uses the Program Property note format
-defined in (`LINUX_ABI`_). An alternative encoding that uses a Arm
-defined Note section called ``.note.AARCH64-PAUTH-ABI-tag`` is defined
-for platforms that do not support Program Properties, or have legacy
-binaries from earlier versions of this specification. This is described
-in `Appendix Alternative ELF Marking Using SHT_NOTE section`_.
-
 Core information
 ----------------
 
@@ -922,15 +917,10 @@ Base Compatibility Model
 A per-ELF file marking scheme permits a coarse way of reasoning about
 compatibility.
 
-* All reasoning about compatibility is done using the `Core Information`_.
-  This permits an ELF file using the ``.note.gnu.property`` ELF marking to
-  be compared to an ELF file using the ``.note.AARCH64-PAUTH-ABI-tag`` ELF
-  marking.
-
-* If an ELF file contains multiple ELF markings of the `Core
-  Information`_, for example it contains both a ``.note.gnu.property``
-  section and a ``.note.AARCH64-PAUTH-ABI-tag`` section, then all
-  must encode the same `Core Information`_.
+* All reasoning about compatibility is done using the `Core
+  Information`_.  This permits an ELF relocatable object file using
+  the ``.note.gnu.property`` ELF marking to be compared to an ELF file
+  using build attributes that encode the `Core Information`_.
 
 * The absence of any ELF marking means no information on how pointers
   are signed is available for this ELF file. When used in combination
@@ -1282,25 +1272,3 @@ Some observations:
 * When not dynamic linking a static linker may choose to encode the
   pointer signing information in a custom encoding understood by the
   start-up code used.
-
-Appendix Alternative ELF Marking Using SHT_NOTE section
-=======================================================
-
-A new section named ``.note.AARCH64-PAUTH-ABI-tag`` of type
-``SHT_NOTE`` is defined. This section is structured as a note section
-as documented in SCO-ELF_, and its attribute flag ``SHF_ALLOC`` must
-be set.
-
-The ``namesz`` field shall be 4
-
-The ``descsz`` field shall be 16. See ``desc`` below.
-
-The type field shall be ``NT_ARM_TYPE_PAUTH_ABI_TAG``, defined to the
-value 1.
-
-The ``name`` field shall be the null-terminated string ``ARM``.
-
-The ``desc`` contain 2 64-bit words. With the first 64-bit word being
-the ``platform identifier``, and the second 64-bit word being the
-``version number``. Both of these form the information required in
-`Core Information`_ above.