You have to pass an object of type bpy.types.Sequence into bpy.types.Sequences.remove(). This means you can pass the return value of sequences.new_effect() into sequences.remove(). In the example in your question that reference would be stored in effName.
bpy.context.scene.sequence_editor.sequences.remove(effName)
If you don't have a reference to the sequence anymore, you will have to retrieve it from:
bpy.context.scene.sequence_editor.sequences_all