bitbake.conf: Remove TERM from default BB_HASHBASE_WHITELIST

Since BitBake commit 0d5cdd0c0d65f2f81c3af0f3767fee86c4142c3a
TERM is no longer preserved in the environment by BitBake, so there
should be no need to whitelist it by default.

Signed-off-by: Jacob Kroon <jacob.kroon@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>