Makefile: remove $(NO_CURL) from $(SCRIPT_DEFINES)

Makefile: remove $(NO_CURL) from $(SCRIPT_DEFINES)

Stop including $(NO_CURL) in $(SCRIPT_DEFINES). The "@NO_CURL@"
replacement added in 6c5c62f3401 (Print an error if cloning a http
repo and NO_CURL is set, 2006-02-15) has not been referenced by
anything in-tree since 49eb8d39c78 (Remove contrib/examples/*,
2018-03-25).

That commit removed the reference from contrib/examples/*, but this
@@NO_CURL@@ hasn't been used since git-pull.sh was the primary entry
point for "git pull".

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>