loose: don't rely on repository global state

loose: don't rely on repository global state

In `loose.c`, we rely on the global variable `the_hash_algo`. As such we
have guarded the file with the 'USE_THE_REPOSITORY_VARIABLE' definition.
Let's derive the hash algorithm from the available repository variable
and remove this guard. This brings us one step closer to removing the
global 'the_repository' variable.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>