fix: Remove post install script which is throwing security warnings in pnpm

The post install is not required as puya will be downloaded on first build if it's missing

Author: tristanmenzel

package.json

@@ -25,7 +25,6 @@
     "build:3-build": "rollup -c --configPlugin typescript",
     "build:4-copy-pkg-json": "tstk copy-package-json -c",
     "build:5-copy-readme": "copyfiles ./README.md ./dist",
-    "build:6-add-postinstall-script": "tsx src/util/add-postinstall-script.ts ./dist",
     "pretest": "tsx src/bin/download-puya-binary.ts",
     "test": "vitest run",
     "test:approvals": "vitest run tests/approvals.spec.ts",