Remove explanatory comments from includes

I noticed a comment by an include and remembered that I think these
don't really provide much value -- sometimes they are just editorial,
and sometimes they are obsolete.  I think it's better to just remove
them.  Tested by rebuilding.

Approved-By: Andrew Burgess <aburgess@redhat.com>

gdb/guile/scm-pretty-print.c

@@ -21,9 +21,9 @@
    conventions, et.al.  */
 
 #include "defs.h"
-#include "top.h"		/* For quit_force().  */
+#include "top.h"
 #include "charset.h"
-#include "symtab.h" /* Needed by language.h.  */
+#include "symtab.h"
 #include "language.h"
 #include "objfiles.h"
 #include "value.h"