Remove code relating to PL_Xpv

This variable is no longer used in any perl code. It used to be used as
a temporary during some expression macros, similar to the way PL_Sv is
used. The last reference I can find to it in real code was removed in
2012, by the commit
  6702ba9

(It's a little late in the 5.39.x development cycle to consider removing
the line from intrpvar.h itself; but we could do that at the start of
5.41.x).

Author: leonerd

embedvar.h

@@ -968,8 +968,6 @@ PERLVAR(I, blockhooks,	AV *)
 
 PERLVAR(I, custom_ops,	HV *)		/* custom op registrations */
 
-PERLVAR(I, Xpv,		XPV *)		/* (unused) held temporary value */
-
 /* name of the scopes we've ENTERed. Only used with -DDEBUGGING, but needs to be
    present always, as -DDEBUGGING must be binary compatible with non.  */
 PERLVARI(I, scopestack_name, const char **, NULL)

intrpvar.h

@@ -3676,7 +3676,6 @@ Perl_perly_sighandler(int sig, Siginfo_t *sip PERL_UNUSED_DECL,
     CV *cv = NULL;
     OP *myop = PL_op;
     U32 flags = 0;
-    XPV * const tXpv = PL_Xpv;
     I32 old_ss_ix = PL_savestack_ix;
     SV *errsv_save = NULL;
 
@@ -3831,7 +3830,6 @@ Perl_perly_sighandler(int sig, Siginfo_t *sip PERL_UNUSED_DECL,
     PL_op = myop;			/* Apparently not needed... */
 
     PL_Sv = tSv;			/* Restore global temporaries. */
-    PL_Xpv = tXpv;
     return;
 }
 

mg.c

@@ -15926,7 +15926,6 @@ perl_clone_using(PerlInterpreter *proto_perl, UV flags,
     PL_op		= proto_perl->Iop;
 
     PL_Sv		= NULL;
-    PL_Xpv		= (XPV*)NULL;
     my_perl->Ina	= proto_perl->Ina;
 
     PL_statcache	= proto_perl->Istatcache;