Flush deprecations before minor release

[pavoljuhas]

• Remove deprecated constants from cirq_google module. Long past the v0.16 deprecation deadline, constants were invalid for almost 2 years after #5762.

• Remove deprecated method cirq_google.Engine.sampler() Long past the v1.0 deprecation deadline.

• Purge deprecated arguments to EngineProcessor.list_calibrations earliest_timestamp_seconds and latest_timestamp_seconds are long past the v1.0 deadline.

• Remove deprecated function cirq_ionq.ionq_devices.decompose_to_device. Long past the v0.16 deadline.

Ref: https://github.com/quantumlib/Cirq/blob/main/release.md#before-you-release-flush-the-deprecation-backlog

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 97.80%. Comparing base (e4b6ab2) to head (ebd99f3). Report is 4 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #6622 +/- ## ========================================== - Coverage 97.81% 97.80% -0.02% ========================================== Files 1063 1061 -2 Lines 91796 91455 -341 ========================================== - Hits 89794 89449 -345 - Misses 2002 2006 +4 ```

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