Remove a batch of deprecated optimizers (quantumlib#5727)

These optimizers have all been migrated to transformers:

Removes:  DropEmptyMoments, DropNegligible, EjectPhasedPauli, EjectZ, ExpandComposite, MergeInteractions, MergeInteractionsAbc, MergeInteractionsToSqrtIswap, and SynchronizeTerminalMeasurements.

Author: dstrain115

cirq/__init__.py

@@ -327,19 +327,7 @@
     ZZPowGate,
 )
 
-from cirq.optimizers import (
-    AlignLeft,
-    AlignRight,
-    ConvertToCzAndSingleGates,
-    DropEmptyMoments,
-    DropNegligible,
-    EjectPhasedPaulis,
-    EjectZ,
-    ExpandComposite,
-    MergeInteractions,
-    MergeInteractionsToSqrtIswap,
-    SynchronizeTerminalMeasurements,
-)
+from cirq.optimizers import AlignLeft, AlignRight, ConvertToCzAndSingleGates
 
 from cirq.transformers import (
     align_left,

cirq/optimizers/__init__.py

@@ -18,24 +18,8 @@
 
 from cirq.optimizers.align_right import AlignRight
 
-from cirq.optimizers.drop_empty_moments import DropEmptyMoments
-
-from cirq.optimizers.drop_negligible import DropNegligible
-
 from cirq.optimizers.convert_to_cz_and_single_gates import ConvertToCzAndSingleGates
 
-from cirq.optimizers.eject_phased_paulis import EjectPhasedPaulis
-
-from cirq.optimizers.eject_z import EjectZ
-
-from cirq.optimizers.expand_composite import ExpandComposite
-
-from cirq.optimizers.merge_interactions import MergeInteractions
-
-from cirq.optimizers.merge_interactions_to_sqrt_iswap import MergeInteractionsToSqrtIswap
-
-from cirq.optimizers.synchronize_terminal_measurements import SynchronizeTerminalMeasurements
-
 from cirq.transformers.analytical_decompositions import (
     compute_cphase_exponents_for_fsim_decomposition,
     decompose_cphase_into_two_fsim,