Remove bogus #include added by d4e71df6d7.

The recently added inclusion of guc.h in smgr.h is not necessary and
introduces more server-related stuff. Removing the directive helps
avoid potential issues with including sgmr.h in frontends.

Author: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Discussion: https://postgr.es/m/20230425.115748.2130383825066921512.horikyota.ntt%40gmail.com

src/include/storage/smgr.h

@@ -17,7 +17,6 @@
 #include "lib/ilist.h"
 #include "storage/block.h"
 #include "storage/relfilelocator.h"
-#include "utils/guc.h"
 
 /*
  * smgr.c maintains a table of SMgrRelation objects, which are essentially