gdb/doc: move @menu to the end of the node

gdb/doc: move @menu to the end of the node

Commit:

  commit a72d0f3d69896b5fcdc916e0547fe774dcb58614
  Date:   Tue Jan 12 13:02:30 2021 +0000

      gdb/doc: reorder and group sections relating to aliases

Added a @menu block into the wrong place within a @node.  This commit
moves it to the end of the @node, where it should be been placed.

gdb/doc/ChangeLog:

	* gdb.texinfo (Aliases): Move @menu to the end of the node.