R1:454ecb56e3ac

When proxying HTTP repository responses from repository nodes, discard content description headers

Summary:
Ref T13517. See that task for details about the underlying issue here.

Currently, we may decode a compressed response, then retransmit it with leftover "Content-Encoding" and "Content-Length" headers. Instead, strip these headers.

Test Plan:
- In a clustered repository setup, cloned a Git repository over HTTP.
- Before: Error while processing content unencoding: invalid stored block lengths…