This changes log statements from log to fs package, which is required for --use-json-log
to properly make log output in JSON format. The recently added custom linting rule,
handled by ruleguard via gocritic via golangci-lint, warns about these and suggests
the alternative. Fixing was therefore basically running "golangci-lint run --fix",
although some manual fixup of mainly imports are necessary following that.
This prevents an `rclone rcd` server from prematurely going into the
'deactivating' state, which was causing systemd to kill it with a
SIGABRT after the stop timeout.
Fixes#7540
