Firestore: Downgrade grpc CocoaPods dependency to 1.44.0 (was 1.50.1)

[dconeybe]

Downgrade grpc CocoaPods dependency to 1.44.0 (was 1.50.1) as a workaround for a Firestore crash on iOS 12 that happens with with grpc 1.50.0 and newer: #11509. Leave the cmake and swift package manager dependencies at 1.50 since they do not experience this crash.

A workaround for this crash is planned to be merged into grpc upstream (grpc/grpc#34416). Once released (and a few other unrelated grpc build issues with Firestore are fixed) the grpc dependency will be re-upgraded to a version that includes the workaround.

Note: This PR effectively reverts #10650.

Fixes #11509

[google-oss-bot]

Coverage Report ¹

Affected Products

• FirebaseFirestore-iOS-FirebaseFirestore.framework

  Overall coverage changed from 88.15% (d9705e6) to 88.16% (8460712) by +0.01%.

  Filename	Base (d9705e6)	Merge (8460712)	Diff
  leveldb_mutation_queue.cc	92.42%	93.56%	+1.14%
  ordered_code.cc	93.90%	94.39%	+0.49%
  task.cc	96.52%	94.78%	-1.74%

Test Logs

• Base (d9705e6): https://github.com/firebase/firebase-ios-sdk/actions/runs/6300798336
• Merge (8460712): https://github.com/firebase/firebase-ios-sdk/actions/runs/6300980585

1. https://storage.googleapis.com/firebase-sdk-metric-reports/zThF84ZoMh.html