Remove hardcoded argument from autoflake linter

The linter is currently hardcoded to do "--remove-all-unused-imports", which
unfortunately does not work for all repos since imports can have side effects.
With this removed a user can still provide the argument if they desire it, but
it is possible to run without it.

src/python/pants/backend/python/lint/autoflake/rules.py

@@ -47,7 +47,6 @@ async def autoflake_fmt(request: AutoflakeRequest, autoflake: Autoflake) -> FmtR
             autoflake_pex,
             argv=(
                 "--in-place",
-                "--remove-all-unused-imports",
                 *autoflake.args,
                 *request.snapshot.files,
             ),