Remove bunch of redundant environ declarations

rpmsign.c used to actually use "environ" to pass to execve(), but
that call moved to librpmsign a long, long time ago. rpmdb.c and
rpmkeys.c never used it at all but guess it was copy-paste inherited
from rpmsign.c back in the day (dfbaa77152)

rpmgensig.c actually refers to environ, but this is a POSIX required
variable and while Apple has managed to screw it up, it's handled
in system.h and that must be sufficient for all relevant systems
as we also refer to environ in rpmfileutil.c open_dso() and there's
no fake environ definition there. So drop the one in rpmgensig.c too.

rpmdb.c

@@ -6,10 +6,6 @@
 #include "cliutils.h"
 #include "debug.h"
 
-#if !defined(__GLIBC__) && !defined(__APPLE__)
-char ** environ = NULL;
-#endif
-
 enum modes {
     MODE_INITDB		= (1 << 0),
     MODE_REBUILDDB	= (1 << 1),

rpmkeys.c

@@ -5,10 +5,6 @@
 #include "cliutils.h"
 #include "debug.h"
 
-#if !defined(__GLIBC__) && !defined(__APPLE__)
-char ** environ = NULL;
-#endif
-
 enum modes {
     MODE_CHECKSIG	= (1 << 0),
     MODE_IMPORTKEY	= (1 << 1),

rpmsign.c

@@ -9,10 +9,6 @@
 #include "cliutils.h"
 #include "debug.h"
 
-#if !defined(__GLIBC__) && !defined(__APPLE__)
-char ** environ = NULL;
-#endif
-
 enum modes {
     MODE_NONE    = 0,
     MODE_ADDSIGN = (1 << 0),

sign/rpmgensig.c

@@ -25,10 +25,6 @@
 
 #include "debug.h"
 
-#if !defined(__GLIBC__) && !defined(__APPLE__)
-char ** environ = NULL;
-#endif
-
 typedef struct sigTarget_s {
     FD_t fd;
     const char *fileName;