grep/pcre2: use compile-time PCREv2 version test

grep/pcre2: use compile-time PCREv2 version test

Replace a use of pcre2_config(PCRE2_CONFIG_VERSION, ...) which I added
in 95ca1f987ed (grep/pcre2: better support invalid UTF-8 haystacks,
2021-01-24) with the same test done at compile-time.

It might be cuter to do this at runtime since we don't have to do the
"major >= 11 || (major >= 10 && ...)" test. But in the next commit
we'll add another version comparison that absolutely needs to be done
at compile-time, so we're better of being consistent across the board.

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