x11-wm/piewm: fix the build with LLVM 11

This patch de-extern'd yylineno to actually cause the build failure that
popped up with the new -fno-common default that debuted in LLVM 11 and GCC
10. Simply remove the patch to fix the build.

PR:		248859
MFH:		2020Q3 (-fno-common build fix)

x11-wm/piewm/files/patch-gram.y

@@ -1,11 +0,0 @@
---- gram.y.orig	Thu Jan  1 15:33:42 1998
-+++ gram.y	Thu Dec  9 23:31:00 1999
-@@ -71,7 +71,7 @@
- extern int do_single_keyword(), do_string_keyword(), do_number_keyword();
- extern name_list **do_colorlist_keyword();
- extern int do_color_keyword();
--extern int yylineno;
-+int yylineno;
- %}
- 
- %union