typing: simplify archive.gz writing and drop a few pytype suppressions
I was waiting until 3.8 to use `Literal` to fix this, but there's also the ":"
and "|" characters that are passed along here, meant only for the non-gz archive
types. But manipulating what the local caller passes is silly- we know we're
writing, so just open it for writing. As an added bonus, PyCharm stops flagging
the call too (since it doesn't know about pytype suppression comments).
(binary:application/octet-stream)