[lldb][test] Remove expectedFailureIfFn (#81703)

Switching to modern `unittest` in
5b386158 needs xfail annotations to be
known prior to test running. In contrast, skipping can happen at any
time, even during test execution.

Thus, `expectedFailureIfFn` inherently doesn't work. Either we eagerly
evaluate the function and use `expectedFailureIf` instead, or we use a
skip annotation to lazily evaluate the function and potentially skip the
test right before it starts.

- For `expectedFailureAndroid`, the intent seems to be that certain
tests _should_ work on android, but don't. Thus, xfail is appropriate,
to ensure the test is re-enabled once those bugs are ever fixed.
- For the other uses in individual tests, those generally seem to be
cases where the test environment doesn't support the setup required by
the test, and so it isn't meaningful to run the test at all. For those,
a drop-in replacement to `skipTestIfFn` works.