Update or remove Crashlytics

[farktronix]

The Crashlytics pod has been deprecated and the replacement is FirebaseCrashlytics. We can either update all our code to use FirebaseCrashlytics, or we could remove that dependency and give the built-in Xcode crash log stuff a try.

@alecgorge - any opinion? Would you be ok if I removed Crashlytics?

[lukeswitz]

Three months, no response. @alecgorge are you out there, do you read me, over