Strip libgtk2 in the target

Rely on the sane default values of Makefile.autotools.in for the
staging and target installs. The immediate benefit is that the target
install will use install-strip instead of install, leading to a quite
nice size reduction in the libraries.

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

package/libgtk2/libgtk2.mk

@@ -9,8 +9,6 @@ LIBGTK2_SITE = ftp://ftp.gtk.org/pub/gtk/2.12
 LIBGTK2_AUTORECONF = NO
 LIBGTK2_INSTALL_STAGING = YES
 LIBGTK2_INSTALL_TARGET = YES
-LIBGTK2_INSTALL_STAGING_OPT = DESTDIR=$(STAGING_DIR) install
-LIBGTK2_INSTALL_TARGET_OPT = DESTDIR=$(TARGET_DIR) install
 
 LIBGTK2_CONF_ENV = ac_cv_func_posix_getpwuid_r=yes glib_cv_stack_grows=no \
 		glib_cv_uscore=no \