Fix flaky test - TestChaosUpload

[Joerger]

Removes call to CheckUploads which was out of place in TestChaosUpload. CheckUploads fails when called concurrently with other calls to CheckUploads and isn't needed in this test.

Before #11551, we didn't see this flaky tests because CheckUploads would always be a noop since no upload would have surpassed the 24 hour grace period within the 2 second test, whereas now CheckUploads is never a noop since the test session uploads aren't tracked by a session tracker.

Fixes the following flaky errors in TestChaosUpload

--- FAIL: TestChaosUpload (0.07s)
    fileasync_chaos_test.go:191: 
        	Error Trace:	fileasync_chaos_test.go:191
        	Error:      	Received unexpected error:
        	           	lock /tmp/teleport-streams1999935953/cc67bbf2-ca87-4176-9547-b9ebe2d5d7d7.tar is acquired by another process
        	Test:       	TestChaosUpload

--- FAIL: TestChaosUpload (0.11s)
    fileasync_chaos_test.go:221: 
        	Error Trace:	fileasync_chaos_test.go:221
        	Error:      	Not equal: 
        	           	expected: 4098
        	           	actual  : 0
        	Test:       	TestChaosUpload
        	Messages:   	event: {aba8002b-345e-413f-a2b5-9fc2d8395685 331c82a6-80b2-40ae-ab8b-9f601f0f93ca <nil> 0001-01-01 00:00:00 +0000 UTC}

--- FAIL: TestChaosUpload (0.15s)
    fileasync_chaos_test.go:202: 
        	Error Trace:	fileasync_chaos_test.go:202
        	Error:      	Received unexpected error:
        	           	lock /tmp/teleport-streams3694352958/fcd138af-26e8-431e-8f0f-4f8bd24c5a06.tar is acquired by another process
        	Test:       	TestChaosUpload
        	Messages:   	
        	           	ERROR REPORT:
        	           	Original Error: *trace.CompareFailedError lock /tmp/teleport-streams3694352958/fcd138af-26e8-431e-8f0f-4f8bd24c5a06.tar is acquired by another process
        	           	Stack Trace:
        	           		/home/bjoerger/gravitational/teleport/lib/utils/fs_unix.go:44 github.com/gravitational/teleport/lib/utils.FSTryWriteLock
        	           		/home/bjoerger/gravitational/teleport/lib/events/filesessions/filestream.go:114 github.com/gravitational/teleport/lib/events/filesessions.(*Handler).CompleteUpload
        	           		/home/bjoerger/gravitational/teleport/lib/events/complete.go:163 github.com/gravitational/teleport/lib/events.(*UploadCompleter).CheckUploads
        	           		/home/bjoerger/gravitational/teleport/lib/events/filesessions/fileasync_chaos_test.go:177 github.com/gravitational/teleport/lib/events/filesessions.TestChaosUpload.func5
        	           		/home/bjoerger/.tools/go/src/runtime/asm_amd64.s:1581 runtime.goexit
        	           	User Message: lock /tmp/teleport-streams3694352958/fcd138af-26e8-431e-8f0f-4f8bd24c5a06.tar is acquired by another process

[zmb3]

Thanks for tracking this down.