ci: Remove one-shot NPM_TOKEN validation workflow

Confirmed via run 25180245112 that the rotated NPM_TOKEN authenticates
as user pmclsf (the owner of the mapterrain package). No further use
for this workflow; deleting before tagging v0.1.2.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: pmclSF