package/zlib-ng: drop unrecognized CC variable

Drop unneeded CC variable which is not recognized by cmake:

CMake Warning:
  Manually-specified variables were not used by the project:

    BUILD_DOC
    BUILD_DOCS
    BUILD_EXAMPLE
    BUILD_EXAMPLES
    BUILD_TEST
    BUILD_TESTING
    BUILD_TESTS
    CC

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/zlib-ng/zlib-ng.mk

@@ -12,7 +12,7 @@ ZLIB_NG_INSTALL_STAGING = YES
 ZLIB_NG_PROVIDES = zlib
 
 # Build with zlib compatible API, gzFile support and optimizations on
-ZLIB_NG_CONF_OPTS += -DZLIB_COMPAT=1 -DWITH_GZFILEOP=1 -DWITH_OPTIM=1 -DCC=$(TARGET_CC)
+ZLIB_NG_CONF_OPTS += -DZLIB_COMPAT=1 -DWITH_GZFILEOP=1 -DWITH_OPTIM=1
 
 # Enable NEON and ACLE on ARM
 ifeq ($(BR2_arm),y)