docs: AUTO_MERGE is not that special

A handful of manual pages called AUTO_MERGE a "special ref", but
there is nothing special about it.  It merely is yet another
pseudoref.

Signed-off-by: Junio C Hamano <[email protected]>

Author: gitster

Documentation/git-diff.txt

@@ -103,7 +103,7 @@ Just in case you are doing something exotic, it should be
 noted that all of the <commit> in the above description, except
 in the `--merge-base` case and in the last two forms that use `..`
 notations, can be any <tree>. A tree of interest is the one pointed to
-by the special ref `AUTO_MERGE`, which is written by the 'ort' merge
+by the ref named `AUTO_MERGE`, which is written by the 'ort' merge
 strategy upon hitting merge conflicts (see linkgit:git-merge[1]).
 Comparing the working tree with `AUTO_MERGE` shows changes you've made
 so far to resolve textual conflicts (see the examples below).

Documentation/git-merge.txt

@@ -196,7 +196,7 @@ happens:
    can inspect the stages with `git ls-files -u`).  The working
    tree files contain the result of the merge operation; i.e. 3-way
    merge results with familiar conflict markers `<<<` `===` `>>>`.
-5. A special ref `AUTO_MERGE` is written, pointing to a tree
+5. A ref named `AUTO_MERGE` is written, pointing to a tree
    corresponding to the current content of the working tree (including
    conflict markers for textual conflicts).  Note that this ref is only
    written when the 'ort' merge strategy is used (the default).

Documentation/user-manual.txt

@@ -1344,7 +1344,7 @@ $ git diff --theirs file.txt	# same as the above.
 -------------------------------------------------
 
 When using the 'ort' merge strategy (the default), before updating the working
-tree with the result of the merge, Git writes a special ref named AUTO_MERGE
+tree with the result of the merge, Git writes a ref named AUTO_MERGE
 reflecting the state of the tree it is about to write. Conflicted paths with
 textual conflicts that could not be automatically merged are written to this
 tree with conflict markers, just as in the working tree. AUTO_MERGE can thus be