ref: remove unnecessary imports

[armcknight]

📜 Description

• don't import <Sentry/Sentry.h> in test code. many were innocuous, some needed the actually tested classes imported
• found an empty test case, removed the file
• removed a few unneeded imports of <XCTest/XCTest.h>

💡 Motivation and Context

There is some weird stuff going on with transitive imports that is breaking some CI jobs in other refactor PRs. Trying to clean it up and cut transitive ties.

#skip-changelog

[codecov]

Codecov Report

Merging #3256 (a21078a) into main (5d6ce0e) will increase coverage by 0.044%.
The diff coverage is n/a.

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #3256       +/-   ##
=============================================
+ Coverage   89.150%   89.195%   +0.044%     
=============================================
  Files          502       501        -1     
  Lines        54113     54114        +1     
  Branches     19428     19418       -10     
=============================================
+ Hits         48242     48267       +25     
+ Misses        5011      4992       -19     
+ Partials       860       855        -5     

Files Changed	Coverage Δ
...s/SentryTests/Helper/SentrySerializationNilTests.m	100.000% <ø> (ø)
Tests/SentryTests/Helper/SentrySwizzleTests.m	89.690% <ø> (ø)
Tests/SentryTests/Networking/SentryDsnTests.m	100.000% <ø> (ø)
Tests/SentryTests/SentryInterfacesTests.m	100.000% <ø> (ø)
...ts/SentryTests/SentryKSCrashReportConverterTests.m	96.978% <ø> (ø)
Tests/SentryTests/SentryNSDataCompressionTests.m	100.000% <ø> (ø)
Tests/SentryTests/SentryScope+Equality.m	28.070% <ø> (ø)
Tests/SentryTests/SentryTests.m	100.000% <ø> (ø)
Tests/SentryTests/TestLogOutput.swift	100.000% <ø> (ø)
...SentryTests/TestUtils/SentryBooleanSerialization.m	100.000% <ø> (ø)

... and 13 files with indirect coverage changes

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[brustolin]

Thanks for doing this.

LGTM