Similar to the preceding commit, drop our use of `write_in_full()` and
implement a new wrapper `reftable_write_full()` that handles this logic
for us. This is done to reduce our dependency on the Git library.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
e31db89558