Issues #10043, #15405, and #22660 appear to have been fixed, and
whatever tests I could run locally do succeed, so remove the skips.

Issue #7237 was closed in favor of #17906, so update its skip line.

Issue #7634 was closed as it had not appeared for over three years.
Re-enable it for now. An issue should be open if the test starts being
skipped again.

Change-Id: I67daade906744ed49223291035baddaad9f56dca
Reviewed-on: https://go-review.googlesource.com/121735
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>