gnutls: remove --with-libz-prefix configure option

The default search path in sysroot is sufficient to find zlib, so the
--with-libz-prefix configure option seems to be unnecessary.

For target builds, relying on sysroot also prevents an absolute path
from being hardcoded in the gnutls.pc pkg-config file.

(From OE-Core rev: 7a800bfeb6c8c83ee7cc74739f496982cd71c8e8)

(From OE-Core rev: f46c2ac0fd05f0e10258d8f03bfb2ebd0c2bcbe3)

Signed-off-by: Andre McCurdy <armccurdy@gmail.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-support/gnutls/gnutls.inc

@@ -23,7 +23,6 @@ EXTRA_OECONF="--disable-rpath \
               --with-included-libtasn1 \
               --enable-local-libopts \
               --with-libpthread-prefix=${STAGING_DIR_HOST}${prefix} \
-              --with-libz-prefix=${STAGING_DIR_HOST}${prefix} \
               --disable-guile \
               --disable-crywrap \
               --without-p11-kit \