21207: Remove FUSE performance tests

21207: Remove FUSE performance tests

None of these tests have been running as intended. The `slow_test`
decorator is written incorrectly such that the return value of
`unittest.skipIf` *replaces* the test method rather than *wrapping* it.

We just did a round of serious performance improvement on FUSE and
literally nobody looked at this code or tried to track down the
profiling results it produces.

I'm not opposed to performance tests on principle. But these tests
aren't that, they just generate some profiling results and then spend a
bunch of time running various checks on the manifest that arv-mount
generated.

Remove them to save runtime and make it easier to run tests under
pytest. We can always write better performance tests later if we want.

Arvados-DCO-1.1-Signed-off-by: Brett Smith <brett.smith@curii.com>