Remove unused variables

Co-authored-by: NSoumyadeep Chakraborty <sochakraborty@pivotal.io>
Co-authored-by: NBen Christel <bchristel@pivotal.io>

gpcontrib/Makefile

@@ -4,8 +4,6 @@ default: all
 
 BLD_TOP=..
 
-GPAUX_DIR=$(BLD_TOP)/gpAux/
-
 ext_dir=$(BLD_TOP)/gpAux/ext
 
 top_builddir = ..

src/backend/Makefile

@@ -17,8 +17,6 @@ subdir = src/backend
 top_builddir = ../..
 include $(top_builddir)/src/Makefile.global
 
-BLD_TOP = $(top_builddir)/gpAux
-
 SUBDIRS = access bootstrap catalog parser commands executor foreign \
 	fts lib libpq main nodes optimizer port postmaster regex \
 	replication rewrite storage tcop tsearch utils $(top_builddir)/src/timezone cdb