httping: remove redundant 'override CFLAGS' patch

It is not necessary to override CFLAGS when CFLAGS is passed through
the environment rather than as an argument to make.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>