Remove unnecessary header from be-secure-gssapi.c

libpq/libpq-be.h is included by libpq/libpq.h so there is no need to
explicitly include it separately.

Author: Daniel Gustafsson
Reviewed-by: Julien Rouhaud
Discussion: https://postgr.es/m/A4852E46-9ED1-4861-A23B-22A83E34A084@yesql.se

src/backend/libpq/be-secure-gssapi.c

@@ -19,7 +19,6 @@
 #include "libpq/auth.h"
 #include "libpq/be-gssapi-common.h"
 #include "libpq/libpq.h"
-#include "libpq/libpq-be.h"
 #include "libpq/pqformat.h"
 #include "miscadmin.h"
 #include "pgstat.h"