Resurrect GDB index generation (RhBug:1410907)

Commit 54d30ac broke GDB index
generation due to a leftover "[". In git master this got fixed in
commit 67d3df3 but we don't want
that on 4.13.x because there are behavior changes involved, so
fixing this specifically on the 4.13.x branch.

scripts/find-debuginfo.sh

@@ -312,7 +312,7 @@ while read nlinks inum f; do
     $strict && exit 2
   fi
 
-  [ type gdb-add-index >/dev/null 2>&1 && gdb-add-index "$f" > /dev/null 2>&1
+  type gdb-add-index >/dev/null 2>&1 && gdb-add-index "$f" > /dev/null 2>&1
 
   # A binary already copied into /usr/lib/debug doesn't get stripped,
   # just has its file names collected and adjusted.