Blender Git Loki

Make polls for removing mesh data layers consistent

This was reported in T90026 for attributes, but was also true for:
- UVMaps
- Vertex Colors
- Sculpt Vertex Colors
- Face Maps

For Vertex groups and Shapekeys this was already done (in that their
remove poll would check if there is a vertex group or shapekey to begin
with), now make this consistent across all mentioned types.

Thx @vvv for the initial patch (where this was done for attributes only)

ref T90026

Reviewed By: HooglyBoogly

Maniphest Tasks: T90026

Differential Revision: https://developer.blender.org/D11990