MB-7629 Remove unused function

src/views/reductions.c: At top level:
src/views/reductions.c:255:13: warning: 'enc_uint48' defined but not used [-Wunused-function]

Change-Id: I0d6d171bcf3c80896ae3f8539169e82a4422e1c8
Reviewed-on: http://review.couchbase.org/25600
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Reviewed-by: Fulu Li <fulu@couchbase.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>