strvec: drop unnecessary include of hex.h

In 41771fa435 (cache.h: remove dependence on hex.h; make other files
include it explicitly, 2023-02-24) we added this as part of a larger
mechanical refactor. But strvec doesn't actually depend on hex.h, so
remove it.

Signed-off-by: Linus Arver <linusa@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

strvec.c

@@ -1,6 +1,5 @@
 #include "git-compat-util.h"
 #include "strvec.h"
-#include "hex.h"
 #include "strbuf.h"
 
 const char *empty_strvec[] = { NULL };