Remove deprecated constants from cirq_google module

Long past the `v0.16` deprecation deadline.
The constant were invalid for almost 2 years after quantumlib#5762.

cirq-google/cirq_google/__init__.py

@@ -15,7 +15,6 @@
 """Classes for working with Google's Quantum Engine API."""
 
 import sys
-from cirq import _compat
 from cirq_google import api
 
 from cirq_google._version import __version__
@@ -114,26 +113,3 @@
 from cirq_google.json_resolver_cache import _class_resolver_dictionary
 
 _register_resolver(_class_resolver_dictionary)
-
-
-_SERIALIZABLE_GATESET_DEPRECATION_MESSAGE = (
-    'SerializableGateSet and associated classes (GateOpSerializer, GateOpDeserializer,'
-    ' SerializingArgs, DeserializingArgs) will no longer be supported.'
-    ' In cirq_google.GridDevice, the new representation of Google devices, the gateset of a device'
-    ' is represented as a cirq.Gateset and is available as'
-    ' GridDevice.metadata.gateset.'
-    ' Engine methods no longer require gate sets to be passed in.'
-    ' In addition, circuit serialization is replaced by cirq_google.CircuitSerializer.'
-)
-
-
-_compat.deprecate_attributes(
-    __name__,
-    {
-        'XMON': ('v0.16', _SERIALIZABLE_GATESET_DEPRECATION_MESSAGE),
-        'FSIM_GATESET': ('v0.16', _SERIALIZABLE_GATESET_DEPRECATION_MESSAGE),
-        'SQRT_ISWAP_GATESET': ('v0.16', _SERIALIZABLE_GATESET_DEPRECATION_MESSAGE),
-        'SYC_GATESET': ('v0.16', _SERIALIZABLE_GATESET_DEPRECATION_MESSAGE),
-        'NAMED_GATESETS': ('v0.16', _SERIALIZABLE_GATESET_DEPRECATION_MESSAGE),
-    },
-)

docs/google/devices.md

@@ -191,8 +191,7 @@ $$
 \right]
 $$
 
-This gate has a duration of 12ns and can be used in `cirq_google.SYC_GATESET`
-or in the `cirq_google.FSIM_GATESET`.
+This gate has a duration of 12ns.
 
 #### Square root of iSWAP
 
@@ -214,8 +213,7 @@ $$
 \right]
 $$
 
-This gate has a duration of 32ns and can be used in
-`cirq_google.SQRT_ISWAP_GATESET` or in the `cirq_google.FSIM_GATESET`.
+This gate has a duration of 32ns.
 
 This gate is implemented by using an entangling gate surrounded by
 Z gates.  The preceding Z gates are physical Z gates and will absorb
@@ -237,15 +235,6 @@ to see if it is available on the processor you are using.
 This gate is equivalent to FSimGate(0, π).  It has an approximate duration
 of 26ns.
 
-#### FSim gateset
-
-The `cirq.FSIM_GATESET` provides all three of the above gates in one set.
-In addition, by using this combined gate set, the FSimGate can be parameterized,
-which allows for efficient sweeps across varying two-qubit gates.
-Note that providing a theta/phi combination that
-is not one of the above gates will cause an error when run on hardware.
-
-
 ### Wait gate
 
 For decay experiments and other applications, a WaitGate is provided

docs/google/engine.md

@@ -193,7 +193,6 @@ engine = cirq_google.Engine(project_id='YOUR_PROJECT_ID')
 # Create a sampler from the engine
 job = engine.run_batch(circuit_list,
                        processor_id='PROCESSOR_ID',
-                       gate_set=cirq_google.FSIM_GATESET,
                        repetitions=1000,
                        params_list=param_list)
 results = job.results()