Remove es _xpack endpoint usage

[jbudz]

With elastic/elasticsearch#35958 most endpoints starting with _xpack are deprecated. We have several areas that need to be updated if we want to avoid filling elasticsearch's deprecations log:

• console
• rollups
• monitoring
• license management
• upgrade assistant
• canvas
• watcher
• telemetry

[jbudz]

#29465 was a partial update, we have #29506 for console

[jbudz]

#29506 is merged so we can close this out. There's a few general use endpoints like _xpack/usage and _xpack/info that are still in use, but this is expected. Plugin specific endpoints should no longer be in use.