net/http: remove Content-Encoding header in roundtrip_js
The fetch api will decode the gzip, but Content-Encoding not be deleted.
To ensure that the behavior of roundtrip_js is consistent with native. delete the Content-Encoding header when the response body is decompressed by js fetch api.
Fixes #63139
Change-Id: Ie35b3aa050786e2ef865f9ffa992e30ab060506e
Reviewed-on: https://go-review.googlesource.com/c/go/+/530155
Commit-Queue: Damien Neil <dneil@google.com> Reviewed-by: Bryan Mills <bcmills@google.com> Reviewed-by: Damien Neil <dneil@google.com>
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Auto-Submit: Damien Neil <dneil@google.com>