manual: Undocument usage of foo.static

foo.static and foo.static() are not expected to work.

Ref: https://github.com/nim-lang/Nim/pull/19084/files#r741203578

doc/manual.rst

@@ -2987,7 +2987,7 @@ Even some code that has side effects is permitted in a static block:
 
   # Below call evaluates the "getNum(123)" at compile time, but its
   # result gets used at run time.
-  echo getNum(123).static
+  echo static(getNum(123))
 
 There are limitations on what Nim code can be executed at compile time;
 see `Restrictions on Compile-Time Execution

tests/system/tstatic_callable.nim

@@ -8,7 +8,5 @@ static:
 
 # Below calls evaluate the "getNum(123)" at compile time, but the
 # results of those calls get used at run time.
-doAssert getNum(123).static == 123
-doAssert getNum(123).static() == 123
 doAssert (static getNum(123)) == 123
 doAssert (static(getNum(123))) == 123