fix: remove a single type hint to retain 2.7.x compatibility (#8799)

Co-authored-by: Hjalti Leifsson <hjaltileifsson@gmail.com>

python/flatbuffers/builder.py

@@ -163,7 +163,7 @@ class Builder(object):
     ## @endcond
     self.finished = False
 
-  def Clear(self) -> None:
+  def Clear(self):
     ## @cond FLATBUFFERS_INTERNAL
     self.current_vtable = None
     self.head = UOffsetTFlags.py_type(len(self.Bytes))