pp_sys: Remove unnecessary uses of sv_mortalcopy.

From evalEmpire/parfait@aa8be68
Author: Michael G. Schwern <schwern@pobox.com>
Date:   Mon Nov 2 18:38:51 2015 -0800

    Remove unnecessary uses of sv_mortalcopy.

    It seems `sv_mortalcopy(&sv_no);` used to be how you created a new SV
    back in 5.000.  The code would do things like this...

           PUSHs(sv = sv_mortalcopy(&sv_no));
           sv_setpvn(sv, hent->h_addr, len);

    Not all of this got converted to use the new macros.

Author: Reini Urban

pp_sys.c

@@ -5032,7 +5032,7 @@ PP(pp_ghostent)
 	if (hent->h_addr)
 	    mPUSHp(hent->h_addr, len);
 	else
-	    PUSHs(sv_mortalcopy(&PL_sv_no));
+	    PUSHs(&PL_sv_no);
 #endif /* h_addr */
     }
     RETURN;
@@ -5532,7 +5532,7 @@ PP(pp_gpwent)
 	mPUSHs(newSVpv(pwent->pw_age, 0));
 #	    else
 	/* I think that you can never get this compiled, but just in case.  */
-	PUSHs(sv_mortalcopy(&PL_sv_no));
+	PUSHs(&PL_sv_no);
 #           endif
 #       endif
 #   endif
@@ -5546,7 +5546,7 @@ PP(pp_gpwent)
 	mPUSHs(newSVpv(pwent->pw_comment, 0));
 #	else
 	/* I think that you can never get this compiled, but just in case.  */
-	PUSHs(sv_mortalcopy(&PL_sv_no));
+	PUSHs(&PL_sv_no);
 #       endif
 #   endif
 
@@ -5625,7 +5625,7 @@ PP(pp_ggrent)
 #ifdef GRPASSWD
 	mPUSHs(newSVpv(grent->gr_passwd, 0));
 #else
-	PUSHs(sv_mortalcopy(&PL_sv_no));
+	PUSHs(&PL_sv_no);
 #endif
 
         sv_setgid(PUSHmortal, grent->gr_gid);