verify-tag: drop signal.h include

There's no reason verify-tag.c needs to include signal.h. It's already
in git-compat-util.h, which we properly include as the first header.
And there doesn't seem to be a particular reason for this include; it's
just an artifact from the file creation in 2ae68fcb (Make verify-tag a
builtin., 2007-07-27).

Likewise verify-commit.c has the same issue, probably because it was
created using verify-tag as a template in d07b00b7 (verify-commit:
scriptable commit signature verification, 2014-06-23).

These includes are probably just redundant, and not hurting anything by
circumventing the order that git-compat-util.h tries to impose, since
we'll always have loaded git-compat-util by the time we get to these. So
this is just a cleanup, and shouldn't fix or break any platforms.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin/verify-commit.c

@@ -12,7 +12,6 @@
 #include "repository.h"
 #include "commit.h"
 #include "run-command.h"
-#include <signal.h>
 #include "parse-options.h"
 #include "gpg-interface.h"
 

builtin/verify-tag.c

@@ -10,7 +10,6 @@
 #include "builtin.h"
 #include "tag.h"
 #include "run-command.h"
-#include <signal.h>
 #include "parse-options.h"
 #include "gpg-interface.h"
 #include "ref-filter.h"