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 cirq-google: Remove SerializableGateSet #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]

Codecov Report

All modified and coverable lines are covered by tests ✅

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

Additional details and impacted files

@@            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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