Remove redundant "make install" from pg_upgrade test suite.

A top-level "make install" includes pg_upgrade since commit
9fa8b0ee.  Back-patch to 9.5, where that
commit first appeared.

src/bin/pg_upgrade/test.sh

@@ -71,7 +71,6 @@ if [ "$1" = '--install' ]; then
 	libdir=$temp_install/$libdir
 
 	"$MAKE" -s -C ../.. install DESTDIR="$temp_install"
-	"$MAKE" -s -C . install DESTDIR="$temp_install"
 
 	# platform-specific magic to find the shared libraries; see pg_regress.c
 	LD_LIBRARY_PATH=$libdir:$LD_LIBRARY_PATH