rust: remove excessive calls to `#[timed]`
This makes trace output *really* noisy and is only useful in case you want to
take a look at a single revlog.
This is easy to add back on a case-by-case basis and does not need to stay with
the more permanent timers.
local test passed
addgroupcopy test passed
clone test passed
lowlevelcopy test passed
slicing test passed
issnapshot test passed
findsnapshot test passed