Remove ENABLE_MATERIAL_U_POPUP flag and cleanup dead code

- removes a lot of dead code for the old popup design and especially around adding notifications to popups
- renames several resource files to remove the material_u specification, as it is now the only design

Test: manually run through launcher popups
Bug: 270395516
Flag: ENABLE_MATERIAL_U_POPUP
Change-Id: I462063482206578b4b896a6d405dc2383f2da510