kv_pair: remove unused kv_pair array functions

These don't seem to be used anywhere, at least not in any published
code, and kv_pair_new_array() appears to misuse calloc() anyway.

BUG=none
BRANCH=none
TEST=ChromeOS compiles for ARM and x86 platforms

Change-Id: Ife3e19dc4b3019251a119336d6c6b77a9de046cf
Signed-off-by: David Hendricks <dhendrix@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/366898
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>