Remove type-ignore for `IReactorTCP.connectTCP`'s `hostname` argument

[DMRobertson]

The fix proposed in #10895 for #10851 requires a series temporary # type: ignore.

We should remove this as soon as we're able: namely, when twisted release a version which includes this commit.

[eshaanagarwal]

hi ! Is this issue open for contribution ?

[DMRobertson]

Hi @eshaanagarwal , a contribution would be welcome, but we can't make progress on this until the twisted project makes a new release. I'll remove the good-first-issue label for now to make that a bit clearer.

[clokep]

Note that "new" in this case means a release after 21.7.0 (which is what the current Twisted release is).