test: FileManager remove perf test (#2869)

CI can't compare the performance test with measure against anything, as Xcode
needs baseline files for the same computer. In CI, the computer specifications might
change frequently, so it's a lot of effort to create those baseline files. This test only
slows down CI, and therefore, we can remove it. For more context see
#1482.

Tests/SentryTests/Helper/SentryFileManagerTests.swift

@@ -375,21 +375,6 @@ class SentryFileManagerTests: XCTestCase {
         XCTAssertEqual(0, fixture.delegate.envelopeItemsDeleted.count)
     }
 
-    /**
-     * We need to deserialize every envelope and check if it contains a session.
-     */
-    func testMigrateSessionInit_WorstCasePerformance() {
-        sut.store(fixture.sessionEnvelope)
-        sut.store(fixture.sessionUpdateEnvelope)
-        for _ in 0...(fixture.maxCacheItems - 3) {
-            sut.store(TestConstants.envelope)
-        }
-
-        measure {
-            sut.store(TestConstants.envelope)
-        }
-    }
-
     func testGetAllEnvelopesAreSortedByDateAscending() {
         givenMaximumEnvelopes()