codecov - fix syntax for excluding code lines from coverage (quantuml…

…ib#6240)

The `coverage` tool understands `# pragma: no cover` markup comments to exclude
code lines from coverage analysis.    The previous syntax `# coverage: ignore`
had no effect and resulted in spurious coverage changes for a different code
paths taken.

Removing the codecov.yml file, because coverage precision had no effect on
codecov complaints about decreased coverage.

cirq/circuits/circuit_operation_test.py

@@ -351,7 +351,7 @@ def test_repeat_zero_times(add_measurements, use_repetition_ids, initial_reps):
 
 
 def test_no_repetition_ids():
-    def default_repetition_ids(self):
+    def default_repetition_ids(self):  # pragma: no cover
         assert False, "Should not call default_repetition_ids"
 
     with mock.patch.object(circuit_operation, 'default_repetition_ids', new=default_repetition_ids):

cirq/transformers/heuristic_decompositions/two_qubit_gate_tabulation.py

@@ -407,8 +407,7 @@ def two_qubit_gate_product_tabulation(
     # If all KAK vectors in the mesh have been tabulated, return.
     missing_vec_inds = np.logical_not(tabulated_kak_inds).nonzero()[0]
 
-    if not np.any(missing_vec_inds):
-        # coverage: ignore
+    if not np.any(missing_vec_inds):  # pragma: no cover
         return TwoQubitGateTabulation(
             base_gate, np.array(kak_vecs), sq_cycles, max_infidelity, summary, ()
         )