sv.c: Rmv redundant clause

If threaded locales are being used, basic locales are too.  No need to
check both

sv.c

@@ -15339,7 +15339,8 @@ perl_clone_using(PerlInterpreter *proto_perl, UV flags,
 
     /* Did the locale setup indicate UTF-8? */
     PL_utf8locale	= proto_perl->Iutf8locale;
-#if defined(USE_LOCALE) && defined(USE_LOCALE_THREADS)
+
+#if defined(USE_LOCALE_THREADS)
     assert(PL_locale_mutex_depth <= 0);
     PL_locale_mutex_depth = 0;
 #endif