remove deprecated defines

- PERL_STATIC_LIBS (was not tested anymore)
- HAVE_GMODULE (always required)
- HAVE_STATIC_IRC
- HAVE_STATIC_PERL
- HAVE_SOCKS (was not working properly)
- USE_GREGEX (we use it)

src/core/iregex.h

@@ -3,20 +3,10 @@
 
 #include <irssi/src/common.h>
 
-#ifdef USE_GREGEX
-
 #include <glib.h>
 typedef	GRegex Regex;
 typedef	struct _MatchInfo MatchInfo;
 
-#else
-
-#include <regex.h>
-typedef	regex_t Regex;
-typedef regmatch_t MatchInfo;
-
-#endif
-
 gboolean
 i_match_info_matches (const MatchInfo *match_info);