Revert "[perl #118747] Allow in-place s///g when !!PL_sawampersand"

This reverts commit 1555b32.

This is causing test failures (not on my machine), and I do not have
time right now to track them all down.

Author: Father Chrysostomos

pp_hot.c

@@ -2159,6 +2159,7 @@ PP(pp_subst)
 	&& !is_cow
 #endif
         && (I32)clen <= RX_MINLENRET(rx)
+        && (once || !(r_flags & REXEC_COPY_STR))
         && !(RX_EXTFLAGS(rx) & RXf_NO_INPLACE_SUBST)
 	&& (!doutf8 || SvUTF8(TARG))
 	&& !(rpm->op_pmflags & PMf_NONDESTRUCT))