Delete obsolete GCI jobs (#1919)
Delete obsolete GCI jobs (#1919)

We are not building m52 and m53 any more.
GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid