test: Remove subclass of NSTimer

[philipphofmann]

We subclassed NSTimer, which is not allowed see:
https://developer.apple.com/documentation/foundation/nstimer#1770465.
This sometimes leads to crashes in TestSentryNSTimerWrapper with EXC_BAD_ACCESS.
The subclass is now removed.

#skip-changelog

[philipphofmann]

cc @armcknight I think that was the reason why the tests sometimes crashed here

sentry-cocoa/SentryTestUtils/TestSentryNSTimerWrapper.swift

Line 25 in 8c50edb

return timer

and not because we used the lazy keyword.

[armcknight]

Huh, could you link to an example of the crash? I haven't seen that one. Good learning though, thanks!

[philipphofmann]

Huh, could you link to an example of the crash? I haven't seen that one. Good learning though, thanks!

I noticed that when running the tests locally, sometimes the tests crashed with EXC_BAD_ACCESS. If you checkout a commit previous to the merge of this PR and run all tests locally a couple of times, you should experience the issue, @armcknight.