Improve PIE794 autofix behavior (#1794)

We now: (1) trigger PIE794 for objects without bases (not sure why this
was omitted before); and (2) remove the entire line, rather than leaving
behind trailing whitespace.

Resolves #1787.

resources/test/fixtures/flake8_pie/PIE794.py

@@ -31,3 +31,10 @@ class User(BaseModel):
     @buzz.setter
     def buzz(self, value: str | int) -> None:
         ...
+
+
+class User:
+    bar: str = StringField()
+    foo: bool = BooleanField()
+    # ...
+    bar = StringField()  # PIE794