chore: remove bulky coverage step from unit tests, remove unit tests from linting presubmit check

.kokoro/presubmit/presubmit.cfg

@@ -1,11 +1,9 @@
 # Format: //devtools/kokoro/config/proto/build.proto
 
-# Run all sessions except system tests and docs builds
-# This only runs unit tests for Python 3.10 since unit tests are required for `cover` to run
-# Other Python version unit tests are run separately
+# Run fast linting and code formatting checks
 env_vars: {
     key: "NOX_SESSION"
-    value: "unit-3.10 lint lint_setup_py blacken cover"
+    value: "lint lint_setup_py blacken"
 }
 
 # Run unit tests in parallel, splitting up by file

noxfile.py

@@ -208,11 +208,6 @@ def default(session):
         "py.test",
         "--quiet",
         f"--junitxml=unit_{session.python}_sponge_log.xml",
-        "--cov=google",
-        "--cov-append",
-        "--cov-config=.coveragerc",
-        "--cov-report=",
-        "--cov-fail-under=0",
         "--ignore=tests/unit/vertex_ray",
         "--ignore=tests/unit/vertex_adk",
         "--ignore=tests/unit/vertex_langchain",