watchman: refactor transport connecting to unconfuse pytype
Pytype sees `self.proc` as potentially `None` here, even though it's set by the
`_connect()` logic. Instead of asserting, simply use the process returned by
that method (which it sets into `self.proc` before returning, so there's no
functional change here).
edition = "2018"
max_width = 79
wrap_comments = true
error_on_line_overflow = true