Fix clippy warnings

[MarkusPettersson98]

This PR fixes recent clippy complaints that are currently hindering CI to become green: 1, 2.

The warning stemming from the objc crate is tricky to fix by keeping objc, as we would have to convert it to a git dependency.. See SSheldon/rust-objc#125 for details on that. What I instead did was to convert the little code we had that used objc to the much more well-maintained objc2 crate which does not generate these clippy warnings. We already have it in our tree because of nseventforwarder, so this change even reduced the total amount of dependencies we have! I see this as an absolute win.

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This change is 

[dlon]

Reviewed 6 of 6 files at r1, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @MarkusPettersson98)

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mullvad-daemon/src/macos_launch_daemon.rs line 29 at r1 (raw file):

/// Implement Objective-C type encoding for the struct. Allows the `objc2` crate
/// to perform function signature matching before performing calls into the Objective-C
/// runtime. This is needed to be able to enable the `verify_message` feature on `objc`.

Nit: This feature doesn't exist anymore

[MarkusPettersson98]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @dlon)

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mullvad-daemon/src/macos_launch_daemon.rs line 29 at r1 (raw file):

Previously, dlon (David Lönnhager) wrote…

Nit: This feature doesn't exist anymore

Soo, should I simply remove the last part of the comment ("This is needed to be able to enable the verify_message feature on objc."), or the entire impl Encode altogether? 🤔

[dlon]

Reviewed 1 of 1 files at r2, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved