Revert "Touch files to save when using overlay, small fixes"

This reverts commit 98b6bd61b675b9d59ee5502b8eee831267dac9c6.
Revert "Save ssl certs too on sysupgrade, use keep.d instead of $TO_SAVE"

This reverts commit d29c9c9af2927e726020b8bbe8a7bbac5b8b4f2c.
Add uhttpd crt and key to TO_SAVE, do touches in sysupgrade when an overlay is present too
Avoid some problems with mounts on sysupgrade