zlib: always build host version dynamically

Host libraries should always be built using dynamic linking, rather than
static if BR2_PREFER_STATIC_LIB is enabled, as that then breaks dependent
libraries expecting a shared library.

Reported-by: Andy Kennedy <andy.kennedy@adtran.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/zlib/zlib.mk

@@ -31,9 +31,7 @@ define HOST_ZLIB_CONFIGURE_CMDS
 	(cd $(@D); rm -rf config.cache; \
 		$(HOST_CONFIGURE_ARGS) \
 		$(HOST_CONFIGURE_OPTS) \
-		CFLAGS="$(ZLIB_PIC)" \
 		./configure \
-		$(ZLIB_SHARED) \
 		--prefix="$(HOST_DIR)/usr" \
 		--sysconfdir="$(HOST_DIR)/etc" \
 	)