Revert "net/http: support gzip, x-gzip Transfer-Encodings"

This reverts commit e6c12c3d.

Reason for revert: the assumption that a T-E of "gzip" implies
"chunked" seems incorrect. The RFC does state that one "MUST apply
chunked as the final transfer coding" but that should be interpreted to
mean that a "chunked" encoding must be listed as the last one, not that
one should be assumed to be there if not. This is confirmed by the
alternative option to chunking on the server side being to "terminate
the message by closing the connection".

The issue seems confirmed by the fact that the code in the body of
#29162 fails with the following error:

    net/http: HTTP/1.x transport connection broken: http: failed to gunzip body: unexpected EOF

This late in the cycle, revert rather than fix, also because we don't
apparently have tests for the correct behavior.

Change-Id: I920ec928754cd8e96a06fb7ff8a53316c0f959e5
Reviewed-on: https://go-review.googlesource.com/c/go/+/215757


Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>