[BRLTTY] Log spamming file system mount error: usbfs

[Samuel Thibault]

Hello,

When the system does not have USB (e.g. virtual machine with not USB),
brltty spams this way:

2025-08-29_09:04:24.53478 daemon.err: Aug 29 10:04:24 brltty[4856]: file system mount error: usbfs[brltty-usbfs] -> /run/brltty/usbfs: No such device

And when it does not have firewire, it spams this way:

2025-08-29_09:11:34.53575 daemon.warn: Aug 29 10:11:34 brltty[4856]: unsupported generic resource identifier: bluetooth:

Could we avoid these warnings in that particular case?

Samuel