We are trying to deprecate gax in favor of api_core, and to do so, we must remove all usage of gax here.

The following libraries still have references/use gax:

• bigtable: only uses gax.metrics, should be trivial to fix. Remove gax usage from BigTable #4873
• datastore: has generated code that uses gax, and hand-written adapter over gapic client. Needs to be regenerated and the adapter code likely needs to be updated (one quick glance, most of it can be removed). Regenerate gapic for datastore and remove gax. #4877
• error reporting: depends on the now-legacy separate gapic package. generated code needs to be co-located. Additionally has a small adapter like datastore which can mostly be removed. Regenerate gapic cilent for error_reporting #4743
• firestore: has generated code that uses gax. Needs to be regenerated. Has two small helpers for remapping gax errors (can be deleted) and adding metadata (will need to just be moved to the callsite). @chemelnucfin made a stab at this in the closed-without-merging PR WIP Firestore: replace gax and regenerate gapic #4880.
• logging: depends on the now-legacy separate gapic package. generated code needs to be co-located. Additionally has an adapter like datastore which can mostly be removed. Generate gapic for logging, remove all references to gax #4759
• spanner: has generated code that uses gax. Needs to be regenerated. Has one helper that adds metadata which can be moved to the callsite. Spanner: Re-generate gapic and drop usage of gax #4695
• speech: has generated code that uses gax, and hand-written adapter over gapic client. Needs to be regenerated and the adapter code likely needs to be updated (one quick glance, most of it can be removed). This also has an error where speech is not a strict alias of speech_v1. Regenerate gapic for Speech API, remove deprecated manual layer #4788
• trace: depends on the now-legacy separate gapic package. generated code needs to be co-located. Additionally has an adapter like datastore which can mostly be removed. Regenerate gapic for Trace and remove dependency on gax #4799