docs: Remove XML-style comments from documentation strings

gtk-doc doesn’t support them any more since it was ported to Markdown,
so they end up appearing in the generated documentation, which isn’t
great.

Mostly, they were used to split up things invisibly, which we can do in
other ways.

Signed-off-by: Philip Withnall <withnall@endlessm.com>
Reviewed-by: nobody

glib/docs.c

@@ -2597,9 +2597,9 @@
  *
  *   membuf = g_malloc (8192);
  *
- *   /<!-- -->* Some computation on membuf *<!-- -->/
+ *   // Some computation on membuf
  *
- *   /<!-- -->* membuf will be automatically freed here *<!-- -->/
+ *   // membuf will be automatically freed here
  *   return TRUE;
  * }
  * ]|