[backport] remove 'CountTable.mget' (nim-lang#13355)

It didn't work, and it was an oversight to be included in v1.0.

(cherry picked from commit 78b15de)

changelog.md

@@ -1,4 +1,4 @@
-# v1.1 - xxxx-xx-xx
+# v1.0.8 - xxxx-xx-xx
 
 
 ## Changes affecting backwards compatibility
@@ -7,6 +7,9 @@
 
 ### Breaking changes in the standard library
 
+- `CountTable.mget` has been removed from `tables.nim`. It didn't work, and it
+  was an oversight to be included in v1.0.
+
 
 
 ### Breaking changes in the compiler

lib/pure/collections/tables.nim

@@ -2239,13 +2239,6 @@ proc `[]`*[A](t: CountTable[A], key: A): int =
   assert(not t.isSorted, "CountTable must not be used after sorting")
   ctget(t, key, 0)
 
-proc mget*[A](t: var CountTable[A], key: A): var int =
-  ## Retrieves the value at ``t[key]``. The value can be modified.
-  ##
-  ## If ``key`` is not in ``t``, the ``KeyError`` exception is raised.
-  assert(not t.isSorted, "CountTable must not be used after sorting")
-  get(t, key)
-
 proc `[]=`*[A](t: var CountTable[A], key: A, val: int) =
   ## Inserts a ``(key, value)`` pair into ``t``.
   ##
@@ -2560,12 +2553,6 @@ proc `[]`*[A](t: CountTableRef[A], key: A): int =
   ##   is in the table
   result = t[][key]
 
-proc mget*[A](t: CountTableRef[A], key: A): var int =
-  ## Retrieves the value at ``t[key]``. The value can be modified.
-  ##
-  ## If ``key`` is not in ``t``, the ``KeyError`` exception is raised.
-  mget(t[], key)
-
 proc `[]=`*[A](t: CountTableRef[A], key: A, val: int) =
   ## Inserts a ``(key, value)`` pair into ``t``.
   ##