95%+ of existing modules enables auto mount (obviously).
Switching auto mount to opt-out makes more sense than opt-in as
in previous module format. The file 'auto_mount' will be ignored, and
the file 'skip_mount' will be checked to toggle the mounting behavior.
After scanning through the current Magisk Module Repo modules, no
modules are using custom bind mounting; all modules with auto mount
disabled have empty system folder, which means this change will not
affect any existing module.
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