Rework PollListBuilder

Problem/Motivation

The PollListBuilder is extending DraggableListBuilder which is a listbuilder for config entities. This doesn't make sense for a few reasons:

• Poll is a content entity, not config
• Why would you want to set the weight on a content overview page?

Steps to reproduce

See: PollListBuilder

Proposed resolution

Update the class to extend a different class. Perhaps EntityListBuilder

Remaining tasks

MR

User interface changes

N/A

API changes

N/A

Data model changes

N/A