transports/meeklite: Use a modified version of utls

Changes:
 * Use a fork of utls with some compatibility improvements.
 * Switch the default ClientHello profile to `HelloFirefox_Auto`.
 * Add the `HelloChrome_71` profile.

The existing `HelloFirefox_Auto` profile that points to
`HelloFirefox_63` also matches the (common) behavior of Firefox 65,
assuming that 3DES ciphersuites are not disabled.