resourceloader: Don't cache CSSMin::remap() calls

resourceloader: Don't cache CSSMin::remap() calls

The output of this function is not deterministic. This function
is what tranforms urls to include content hashes and also embeds
content as data URI. The calls to this function are expected to be
up to date and matching the version hash as constructed by the
current web request.

Previously, the content hash as constructed based on the collective
file hash of all references images was accurate but the generated
css associated with it could be stale.

Unless we abuse MemoizedCallable to take a separate cache buster
(with $localFileRefs?), it's best to remove this as it isn't
a deterministic function and shouldn't be memoized.

Bug: T128668
Change-Id: Icb87ddc585d7320ac48619446bb8b9cbe5f4780e