Remove unused includes in infcmd.c and infrun.c

Remove unused includes in infcmd.c and infrun.c

include-what-you-use reported this:

../../../src/binutils-gdb/gdb/infcmd.c should remove these lines:
- #include <signal.h>  // lines 22-22
- #include "cli/cli-decode.h"  // lines 48-48
- #include "cli/cli-utils.h"  // lines 56-56
- #include "event-top.h"  // lines 38-38
- #include "infcall.h"  // lines 57-57
- #include "parser-defs.h"  // lines 39-39

../../../src/binutils-gdb/gdb/infrun.c should remove these lines:
- #include <signal.h>  // lines 37-37
- #include "cli/cli-script.h"  // lines 31-31
- #include "continuations.h"  // lines 54-54
- #include "dictionary.h"  // lines 45-45
- #include "gdbsupport/gdb_wait.h"  // lines 28-28
- #include "interps.h"  // lines 55-55

Remove those includes.

Tested by rebuilding, and by quick inspection that the include fields
were indeed unnecessary.

gdb/ChangeLog:

	* infcmd.c: Remove includes.
	* infrun.c: Remove includes.

Change-Id: I5e25af54ecd2235960c4127add8f604ddbb19153