Get rid of confusing FUSE variables and comments.

Long before scoped storage, FUSE was used to create several views of the
filesystem; this was later replaced by sdcardfs, yet the code still
references FUSE in variables and log messages. Fix those up to avoid
confusion with the "new FUSE".

Bug: 135341433
Test: atest AdoptableHostTest
Change-Id: I2966c5f95d6f38df36a20cdfdd0b95b3051f3f1e
4 files changed