ksud: fix /debug_ramdisk not mounting

[bryanyee33]

Bring back mount_tmpfs() in
https://github.com/tiann/KernelSU/blob/a3df721b845f288a731916fc7777efeefb033af7/userspace/ksud/src/mount.rs#L158
to allow both legacy and new implementations.

This fixes /debug_ramdisk not mounting for certain devices on magic mount.

Reference to original usage in KernelSU:
https://github.com/tiann/KernelSU/blob/69f31abd62e4f275bb33c9b478961d09231f154d/userspace/ksud/src/init_event.rs#L194

mount.rs which was brought back in bff23c6 is now unused so it can also be safely removed.

[rifsxd]

This should already handle tmpfs

5ec1cff@76bfccd#diff-48e226c54c25bf8f36adb4bca81530d4d5edb2fc863f67ef1ea242dee068473fR70

[bryanyee33]

No that commit is to allow toggling of mounting /debug_ramdisk.
Some users do not have /debug_ramdisk mounted on boot, and are unable to add/modify files inside even with root.
The error shows up as "Read-only file system" instead
of "Permission denied", showing that the mount is not simply hidden.

I've got 2 different methods to possibly fix it currently:
bryanyee33@b8e38b7
bryanyee33@f2dedcc

but the user with the issue has not gotten back to me yet.

[rifsxd]

when you've finished testing and debugging this issue then let me know