Throw out old HTTPFile->size code and use LWP

Throw out old HTTPFile->size code and use LWP

The old file size check code was a mess. It had missleading errors, such as
saying a path failed with it couldn't connect to a side channel.

I'm also completely dubious of the continued automatic non-optional use of the
size checking sidechannel. Users with nginx or apache backends are better
served using HTTP HEAD requests against those, even if they use mogstored for
PUT's or usage file generation.