BuildRequires: s/postgresql-devel/libpq-devel/

That's because we moved libpq.so.5 into libpq package.  Also drop
the PGRPMs support to not overcomplicate this patch.

Related: rhbz#1618698, rhbz#1623764

grass.spec

@@ -49,11 +49,10 @@ BuildRequires:	netcdf-devel
 %endif
 BuildRequires:	python < 3.0
 BuildRequires:	python2-numpy
-%if (0%{?rhel} > 6 || 0%{?fedora})
+%if 0%{?rhel} && 0%{?rhel} <= 7
 BuildRequires:	postgresql-devel
 %else
-# RHEL6: PG from http://yum.postgresql.org/9.6/redhat/rhel-$releasever-$basearch/
-BuildRequires:  postgresql96-devel postgresql96-libs
+BuildRequires:	libpq-devel
 %endif
 BuildRequires:	proj-devel
 BuildRequires:	proj-epsg
@@ -188,12 +187,7 @@ export GRASS_PYTHON="/usr/bin/python2"
 %else
 	--with-mysql-libs=%{_libdir}/mysql \
 %endif
-%if (0%{?rhel} > 6 || 0%{?fedora})
-        --with-postgres-includes=%{_includedir}/pgsql \
-%else
-	--with-postgres-includes=%{_prefix}/pgsql-9.6/include/ \
-	--with-postgres-libs=%{_prefix}/pgsql-9.6/lib/ \
-%endif
+	--with-postgres-includes=%{_includedir}/pgsql \
 	--with-cairo-ldflags=-lfontconfig \
 	--with-freetype-includes=%{_includedir}/freetype2 \
 	--with-proj-share=%{_datadir}/proj