Revert "core/mount: minimize impact on mount storm."

Revert "core/mount: minimize impact on mount storm."

This reverts commit 89f9752ea08f516b5d77f8e577bb772073c70c01.

This patch causes various problems during boot, where a "mount storm" occurs
naturally. Current approach is flakey, and it seems very risky to push a
feature like this which impacts boot right before a release. So let's revert
for now, and consider a more robust solution after later.

Fixes #11209.

> https://github.com/systemd/systemd/pull/11196#issuecomment-448523186:
"Reverting 89f9752ea08f516b5d77f8e577bb772073c70c01 and fcfb1f775ed0e9d282607bb118ba788b98952855 fixes this test."