mailmap, quote: move declarations of global vars to correct unit

mailmap, quote: move declarations of global vars to correct unit

Since earlier commits removed the inclusion of cache.h from mailmap.c
and quote.c, it feels odd to have the extern declarations of
global variables in cache.h rather than the actual header included
by the source file.  Move these global variable extern declarations
from cache.h to mailmap.c and quote.c.

Signed-off-by: Elijah Newren <newren@gmail.com>
Acked-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>