gnutls: remove unrecognized --with-libnettle-prefix

configure: WARNING: unrecognized options: --disable-docs, --disable-documentation, --with-xmlto, --with-fop, --enable-ipv6, --with-libnettle-prefix

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/gnutls/gnutls.mk

@@ -18,7 +18,6 @@ GNUTLS_CONF_OPTS = \
 	--disable-rpath \
 	--enable-local-libopts \
 	--enable-openssl-compatibility \
-	--with-libnettle-prefix=$(STAGING_DIR)/usr \
 	--with-librt-prefix=$(STAGING_DIR) \
 	--without-tpm \
 	$(if $(BR2_PACKAGE_GNUTLS_TOOLS),--enable-tools,--disable-tools)