chore(ui-tooling): drop the changeset polarity census and its alias

The census was the instrument for objectui#9727, closed after the
rebuild; no gate, workflow or document runs it. Its test and fixture
corpus went in the previous slice, so this removes the script and the
`census:changeset-polarity` alias, the only remaining reference.

Co-authored-by: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012eXtKYmXEnCc1GExP4go12

Author: claude

ui/package.json

@@ -51,7 +51,6 @@
     "census:tsconfig-test-parity": "node scripts/tsconfig-test-parity-census.mjs",
     "census:cross-file-line-citations": "node scripts/cross-file-line-citation-census.mjs",
     "census:dollar-dialect-aliases": "node scripts/dollar-dialect-alias-census.mjs",
-    "census:changeset-polarity": "node scripts/changeset-polarity-census.mjs",
     "check:new-line-citations": "node scripts/check-new-cross-file-line-citations.mjs",
     "check:control-bytes": "node scripts/check-control-bytes.mjs",
     "check:published-dist": "node scripts/check-published-dist-tooling.mjs",