[python/pyre.vim] use pyrefly executable (#4972)

https://github.com/facebook/pyrefly

The pyre project has evolved to pyrefly. This replaces the pyre linter
with a pyrefly one and removes the test files that were added for
finding the project root in the old pyre world.

Co-authored-by: Oliver Ruben Albertini <oliverruben@gmail.com>

doc/ale-supported-languages-and-tools.txt

@@ -545,6 +545,7 @@ Notes:
   * `pylint`!!
   * `pylsp`
   * `pyre`
+  * `pyrefly`
   * `pyright`
   * `refurb`
   * `reorder-python-imports`