c2n was already a conditional feature, but it didn't have a
feature/c2n directory before (rather, it was using consts + DCE). This
adds it, and moves some code, which removes the httprec dependency.
Also, remove some unnecessary code from our httprec fork.
Updates #12614
Change-Id: I2fbe538e09794c517038e35a694a363312c426a2
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
The c2n handling code was using the Go httptest package's
ResponseRecorder code but that's in a test package which brings in
Go's test certs, etc.
This forks the httptest recorder type into its own package that only
has the recorder and adds a test that we don't re-introduce a
dependency on httptest.
Updates #12614
Change-Id: I3546f49972981e21813ece9064cc2be0b74f4b16
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
