nginx: drop redundant --with-cc-opt configure arg

Drop redundant --with-cc-opt configure arg to mute warning of
cc1: note: someone does not honour COPTS correctly, passed 2 times.

CFLAGS are already parsed and correctly applied without this option and
adding it just makes the CFLAGS appended twice.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>

net/nginx/Makefile

@@ -406,7 +406,6 @@ CONFIGURE_ARGS += \
 	--http-proxy-temp-path=/var/lib/nginx/proxy \
 	--http-fastcgi-temp-path=/var/lib/nginx/fastcgi \
 	--with-cc="$(TARGET_CC)" \
-	--with-cc-opt="$(TARGET_CPPFLAGS) $(TARGET_CFLAGS)" \
 	--with-ld-opt="$(TARGET_LDFLAGS)" \
 	--without-http_upstream_zone_module \
 	--with-compat \