WIP: Remove duplicate escaping from branch dropdown

What does this MR do?

Remove one of the two places where branch names are escaped from the switch branch dropdown.

Why was this MR needed?

Branch names were escaped twice such that switching branch didn't work for certain branch names (e.g. feature/#1234).

• first place: escape()
• second place: $form.serialize()

see also https://jsfiddle.net/mep7v3rz/

What are the relevant issue numbers?

fixes #21248 (closed), #20759 (closed)

cc @smcgivern