chore(revert): use gapic-generator-python 1.0.0 (#696)

* Revert "chore: use gapic-generator-python 1.0.0 (#691)"

This reverts commit fb493bd4b20da58a5224a154cc906df273327181.

* 🦉 Updates from OwlBot post-processor

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

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: parthea

packages/google-cloud-pubsub/noxfile.py

@@ -215,35 +215,19 @@ def default(session):
     install_unittest_dependencies(session, "-c", constraints_path)
 
     # Run py.test against the unit tests.
-    if session.python != "3.6":
-        session.run(
-            "py.test",
-            "--quiet",
-            "--asyncio-mode=strict",
-            f"--junitxml=unit_{session.python}_sponge_log.xml",
-            "--cov=google/cloud",
-            "--cov=tests/unit",
-            "--cov-append",
-            "--cov-config=.coveragerc",
-            "--cov-report=",
-            "--cov-fail-under=0",
-            os.path.join("tests", "unit"),
-            *session.posargs,
-        )
-    else:
-        session.run(
-            "py.test",
-            "--quiet",
-            f"--junitxml=unit_{session.python}_sponge_log.xml",
-            "--cov=google/cloud",
-            "--cov=tests/unit",
-            "--cov-append",
-            "--cov-config=.coveragerc",
-            "--cov-report=",
-            "--cov-fail-under=0",
-            os.path.join("tests", "unit"),
-            *session.posargs,
-        )
+    session.run(
+        "py.test",
+        "--quiet",
+        f"--junitxml=unit_{session.python}_sponge_log.xml",
+        "--cov=google/cloud",
+        "--cov=tests/unit",
+        "--cov-append",
+        "--cov-config=.coveragerc",
+        "--cov-report=",
+        "--cov-fail-under=0",
+        os.path.join("tests", "unit"),
+        *session.posargs,
+    )
 
 
 @nox.session(python=UNIT_TEST_PYTHON_VERSIONS)