MLKit update in 6.26.0 introduced symbol collisions with Firestore and FirebasePerformance

MLKit updated its TensorFlowLiteC dependency to 2.2 which links in `abseil` symbols instead of using its CocoaPod.

Details at https://github.com/firebase/firebase-ios-sdk/runs/737463642?check_suite_focus=true#step:5:2112

The symbol collision tests disabled in #5872 should be reenabled when this is fixed.