isl: remove INSTALL_STAGING = YES

The package is host-only, so there's no point in specifying
INSTALL_STAGING = YES.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/isl/isl.mk

@@ -12,7 +12,6 @@ ISL_SOURCE = isl-$(ISL_VERSION).tar.bz2
 ISL_SITE = http://isl.gforge.inria.fr/
 ISL_LICENSE = MIT
 ISL_LICENSE_FILES = LICENSE
-ISL_INSTALL_STAGING = YES
 ISL_DEPENDENCIES = gmp
 
 # Our libtool patch doesn't apply, and since this package is only