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>

gdbsupport/gdb_wait.h

@@ -20,10 +20,10 @@
 #define COMMON_GDB_WAIT_H
 
 #ifdef HAVE_SYS_WAIT_H
-#include <sys/wait.h> /* POSIX */
+#include <sys/wait.h>
 #else
 #ifdef HAVE_WAIT_H
-#include <wait.h> /* legacy */
+#include <wait.h>
 #endif
 #endif