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>