🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

Author: gcf-owl-bot[bot]

noxfile.py

@@ -294,18 +294,8 @@ def install_systemtest_dependencies(session, *constraints):
 
 
 @nox.session(python=SYSTEM_TEST_PYTHON_VERSIONS)
-@nox.parametrize(
-    "protobuf_implementation,database_dialect",
-    [
-        ("python", "GOOGLE_STANDARD_SQL"),
-        ("python", "POSTGRESQL"),
-        ("upb", "GOOGLE_STANDARD_SQL"),
-        ("upb", "POSTGRESQL"),
-        ("cpp", "GOOGLE_STANDARD_SQL"),
-        ("cpp", "POSTGRESQL"),
-    ],
-)
-def system(session, protobuf_implementation, database_dialect):
+@nox.parametrize("database_dialect", ["GOOGLE_STANDARD_SQL", "POSTGRESQL"])
+def system(session, database_dialect):
     """Run the system test suite."""
     constraints_path = str(
         CURRENT_DIRECTORY / "testing" / f"constraints-{session.python}.txt"
@@ -339,12 +329,6 @@ def system(session, protobuf_implementation, database_dialect):
 
     install_systemtest_dependencies(session, "-c", constraints_path)
 
-    # TODO(https://github.com/googleapis/synthtool/issues/1976):
-    # Remove the 'cpp' implementation once support for Protobuf 3.x is dropped.
-    # The 'cpp' implementation requires Protobuf<4.
-    if protobuf_implementation == "cpp":
-        session.install("protobuf<4")
-
     # Run py.test against the system tests.
     if system_test_exists:
         session.run(
@@ -354,7 +338,6 @@ def system(session, protobuf_implementation, database_dialect):
             system_test_path,
             *session.posargs,
             env={
-                "PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION": protobuf_implementation,
                 "SPANNER_DATABASE_DIALECT": database_dialect,
                 "SKIP_BACKUP_TESTS": "true",
             },
@@ -367,7 +350,6 @@ def system(session, protobuf_implementation, database_dialect):
             system_test_folder_path,
             *session.posargs,
             env={
-                "PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION": protobuf_implementation,
                 "SPANNER_DATABASE_DIALECT": database_dialect,
                 "SKIP_BACKUP_TESTS": "true",
             },
@@ -587,4 +569,4 @@ def prerelease_deps(session, protobuf_implementation, database_dialect):
                 "SPANNER_DATABASE_DIALECT": database_dialect,
                 "SKIP_BACKUP_TESTS": "true",
             },
-        )
+        )