The upstream crypto package now supports sending banners at any time during
authentication, so the Tailscale fork of crypto/ssh is no longer necessary.
github.com/tailscale/golang-x-crypto is still needed for some custom ACME
autocert functionality.
tempfork/gliderlabs is still necessary because of a few other customizations,
mostly related to TTY handling.
Originally implemented in 46fd4e58a2,
which was reverted in b60f6b849a to
keep the change out of v1.80.
Updates #8593
Signed-off-by: Percy Wegmann <percy@tailscale.com>