Remove Makefile. Now generated by configure.

Makefile

-# The Postgres make files exploit features of GNU make that other makes
-# do not have.  Because it is a common mistake for users to try to build
-# Postgres with a different make, we have this make file that does nothing
-# but tell the user to use GNU make.
-
-# If the user were using GNU make now, this file would not get used because
-# GNU make uses a make file named "GNUmakefile" in preference to "Makefile"
-# if it exists.  Postgres is shipped with a "GNUmakefile".
-
-all install clean dep depend distclean:
-	@echo "You must use GNU make to use Postgres.  It may be installed"
-	@echo "on your system with the name 'gmake'."
-	@echo
-	@echo "NOTE:  If you are sure that you are using GNU make and you are"
-	@echo "       still getting this message, you may simply need to run"
-	@echo "       the configure program."