simplify: Minor refactoring
simplify: Minor refactoring

This change renames vertex_remap to collapse_remap to reduce ambiguity
with remap tables, and adds an early-out when no collapses can be found.

The no-collapse issue can't happen right now because we don't restrict
collapses, but it will become important once we lock certain vertices.

Also change kind type to unsigned char to avoid "indexing using char"
warning.

zeux/meshoptimizer,zeux/meshoptimizer,zeux/meshoptimizer