Revert "Modify ${CPPFLAGS} to add pg_config's setting for PGINCLUDEDIR to the"

This reverts commit 77fa8494dd.

Makefile.global.in already handles PGINCLUDEDIR -- the problem is
incorrect #include statements in some of the sources.

configure.in

@@ -58,9 +58,6 @@ SAVE_CFLAGS="$CFLAGS"
 AC_PROG_CC([$($PG_CONFIG --cc)])
 CFLAGS="$SAVE_CFLAGS"
 
-# Add the Postgres PKGINCLUDEDIR to the include search path
-CPPFLAGS="$CPPFLAGS -I$($PG_CONFIG --pkgincludedir)"
-
 # check for a number of CFLAGS that make development easier
 
 # CITUSAC_PROG_CC_CFLAGS_OPT