fix(deprecation warnings): Fix deprecation warnings

[JanNash]

Summary

This PR

• fixes deprecation warnings for iOS 12.0 and 13.0, tvOS 11.0
• adds a diagnostic ignored around the usage of the function CC_MD5, which was deprecated in iOS 13.0 but is only used for the checksum field, thus it should be fine to silence the warning

Checklist

• Does your PR title have the correct title format?
• Does your PR have a breaking change?: no

[JanNash]

The tvOS test testMergeEventsAndIdentifys failed, have you possibly seen this error before?

2020-10-19 21:27:46.195269+0000 xctest[1289:15132] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'No partial mock for object 0x7f8a77e8e4b0'
*** First throw call stack:
(
	0   CoreFoundation                      0x00007fff207526ce __exceptionPreprocess + 242
	1   libobjc.A.dylib                     0x00007fff20090f78 objc_exception_throw + 48
	2   CoreFoundation                      0x00007fff207525ac -[NSException initWithCoder:] + 0
	3   Amplitude_tvOSTests                 0x0000000109351f4f -[OCPartialMockObject classForRealObject] + 95
	4   libobjc.A.dylib                     0x00007fff200a7ce2 -[NSObject isKindOfClass:] + 22
	5   CFNetwork                           0x00007fff20d516f3 _CFHTTPMessageSetResponseProxyURL + 16465
	6   CFNetwork                           0x00007fff20d4f9d8 _CFHTTPMessageSetResponseProxyURL + 9014
	7   libdispatch.dylib                   0x00007fff2017e35b _dispatch_call_block_and_release + 12
	8   libdispatch.dylib                   0x00007fff2017f534 _dispatch_client_callout + 8
	9   libdispatch.dylib                   0x00007fff20185425 _dispatch_lane_serial_drain + 715
	10  libdispatch.dylib                   0x00007fff20185fd7 _dispatch_lane_invoke + 458
	11  libdispatch.dylib                   0x00007fff20190591 _dispatch_workloop_worker_thread + 782
	12  libsystem_pthread.dylib             0x00007fff49ca8a3d _pthread_wqthread + 290
	13  libsystem_pthread.dylib             0x00007fff49ca7b77 start_wqthread + 15
)
libc++abi.dylib: terminating with uncaught exception of type NSException
2020-10-19 21:28:01.818 xcodebuild[1084:11509]  IDETestOperationsObserverDebug: Writing diagnostic log for test session to:
/Users/runner/Library/Developer/Xcode/DerivedData/Amplitude-bviytnhbmawyrdhbsphnwdwgqweg/Logs/Test/Test-Amplitude_tvOS-2020.10.19_21-27-24-+0000.xcresult/Staging/1_Test/Diagnostics/Amplitude_tvOSTests-E699FF2F-220F-463E-95F6-29097875C9C6/Amplitude_tvOSTests-3B38C976-66A4-406C-8E00-E0029DA83A80/Session-Amplitude_tvOSTests-2020-10-19_212801-gHOQMi.log
2020-10-19 21:28:01.818 xcodebuild[1084:11271] [MT] IDETestOperationsObserverDebug: (5C9A4B37-1E91-4B83-921B-0F158F9CFDF5) Beginning test session Amplitude_tvOSTests-5C9A4B37-1E91-4B83-921B-0F158F9CFDF5 at 2020-10-19 21:28:01.818 with Xcode 12A7209 on target <DVTiPhoneSimulator: 0x7fabc620c8b0> {
		SimDevice: Apple TV (DF6775A2-7B9F-4DC9-B3A0-7050A6D96E5A, tvOS 14.0, Booted)
} (14.0 (18J383))
2020-10-19 21:28:01.820 xcodebuild[1084:11271] [MT] IDETestOperationsObserverDebug: (5C9A4B37-1E91-4B83-921B-0F158F9CFDF5) Finished requesting crash reports. Continuing with testing.

Restarting after unexpected exit, crash, or test timeout in AmplitudeTests/testMergeEventsAndIdentifys; summary will include totals from previous launches.

[haoliu-amp]

@JanNash We do see some flaky tests after refining our build pipelines. We're working on fixing them.

@jooohhn Could you take a look when you get a chance?

[haoliu-amp]

Only one nit, others lgtm.