xerces: enable parallel builds

It seems to be in place for historical reasons since it seems to build
just fine on my test rigs.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/xerces/xerces.mk

@@ -9,7 +9,6 @@ XERCES_SOURCE = xerces-c-$(XERCES_VERSION).tar.xz
 XERCES_SITE = http://archive.apache.org/dist/xerces/c/3/sources
 XERCES_LICENSE = Apache-2.0
 XERCES_LICENSE_FILES = LICENSE
-XERCES_MAKE = $(MAKE1)
 XERCES_INSTALL_STAGING = YES
 XERCES_CONF_OPTS = \
 	--disable-threads \