Remove test session cache to reduce possible concurrent problem (#22199) (#22429)

backport #22199

tests/integration/signout_test.go

@@ -22,7 +22,4 @@ func TestSignOut(t *testing.T) {
 	// try to view a private repo, should fail
 	req = NewRequest(t, "GET", "/user2/repo2")
 	session.MakeRequest(t, req, http.StatusNotFound)
-
-	// invalidate cached cookies for user2, for subsequent tests
-	delete(loginSessionCache, "user2")
 }