Commit b6eb8dff649b0f46c12d24e89aa11254fb0132fa renamed compression
setting environment variables to follow consistent style.
Although it preserved backward compatibility for the most part (i.e. it
handled MINIO_COMPRESS_ALLOW_ENCRYPTION, MINIO_COMPRESS_EXTENSIONS, and
MINIO_COMPRESS_MIME_TYPES), MINIO_COMPRESS_ENABLE was left behind.
Additionally, due to incorrect fallback ordering, and DefaultKVS
containing enable=off allow_encryption=off (so kvs.Get should've been
tried last), that commit broke MINIO_COMPRESS_ALLOW_ENCRYPTION (even
though it appeared to be handled), and even older MINIO_COMPRESS, too.
The legacy MIME types and extensions variables take precedence over both
config and new variables, so they don't need fixing.