gdb: small cleanup in breakpoint.c's includes

gdb: small cleanup in breakpoint.c's includes

In an attempt to reduce the number of files re-build when some headers
are touched, I ran include-what-you-use with breakpoint.c as a guinea
pig.  It revealed a few files that were unnecessary to include, which
this patch removes.

breakpoint.c uses tilde_expand from readline, hence the necessity to
include tilde.h.  AFAIK, it's fine to include just that, and not the
whole readline headers.

include-what-you-use also reported many header files that should be
included but aren't, I suppose that breakpoint.c currently includes them
indirectly.  For now I'll pretend I didn't see that :).

gdb/ChangeLog:

	* breakpoint.c: Remove some includes: continuations.h, skip.h,
	mi/mi-main.h, readline/readline.h, readline/history.h.  Add
	include: readline/tilde.h.

-#include "skip.h"
 #include "ax-gdb.h"
 #include "dummy-frame.h"
 #include "interps.h"
@@ -69,11 +67,9 @@
 #include "thread-fsm.h"
 #include "tid-parse.h"
 #include "cli/cli-style.h"
-#include "mi/mi-main.h"

 /* readline include files */
-#include "readline/readline.h"
-#include "readline/history.h"
+#include "readline/tilde.h"

 /* readline defines this.  */
 #undef savestring

Change-Id: I88bfe9071f2f973fd84caaf04b95c33a4dfb33de