Don't delete content-length before yielding inflate body

[st0012]

Fixes #49

result when running the same repro script

❯ time ruby -Ilib -rnet/http -rdebug -e "puts Net::HTTP.get(URI.parse('https://raw.githubusercontent.com/ruby/debug/master/.gitignore'))"
/.bundle/
/.yardoc
/_yardoc/
/coverage/
/doc/
/pkg/
/spec/reports/
/tmp/
*.bundle
/Gemfile.lock
/lib/debug/debug.so
.ruby-version
/debugAdapterProtocol.json
/chromeDevToolsProtocol.json
ruby -Ilib -rnet/http -rdebug -e   0.24s user 0.10s system 57% cpu 0.606 total

The content-length information is still needed when evaluating the given block. Removing it before that will make read_body_0 switch from @socket.read length to @socket.read_all, which can take very long and cause timeout.

I'm not sure how to reproduce the issue with tests though.

[st0012]

@jeremyevans I'm not familiar with the net-http's implementation so this may not be the best solution. If that's the case, feel free to close it 🙂

[jeremyevans]

I've tested this this fixes Ruby CI, and incorporated the fix in #51. Thanks @st0012!