chore!(gax): upgrade to google/longrunning:v1, remove deprecated classes and methods

[bshaffer]

Moves changes in googleapis/gax-php#660 to monorepo

A new major version of GAX is required in order to move off the previous LongRunning client classes (see #9018).

In addition to removing the deprecated LongRunning client classes, a new version of GAX should do the following:

• address feat: add strict types to all class files gax-php#435
• consider removing google/grpc-gcp dependency
• consider removing or moving src/Testing
• remove support for previous client surfaces
• tighten nullable typehints and implement interfaces from Feature Request: Implement interfaces for GAPIC service classes gapic-generator-php#813