Since 78f28b55d3, allocating on multiple threads is much
faster, making it a nice improvement to parallelize vertex group
operations. This patch adds multi-threading when removing a
vertex group from the "Remove Named Attribute" node.
On a Ryzen 3700x:
Before: `(Average: 15.6 ms, Min: 15.0 ms)`
After: `(Average: 8.1 ms, Min: 7.6 ms)`
Differential Revision: https://developer.blender.org/D16916