chore: remove obsolete bootstrap stub files

Remove old bootstrap implementation files that have been superseded
by the new esbuild-based bootstrap in packages/socket.

Removed:
- packages/cli/src/stub/bootstrap.mts (old SEA bootstrap)
- packages/cli/src/stub/npm-package/ (npm wrapper stub)
- packages/socket/bin/bootstrap.js (old bootstrap)
- packages/socket/bin/socket.js (old entry point)

The new bootstrap is built from packages/socket/src/bootstrap.mts
and output to packages/socket/dist/bootstrap.js.

Author: jdalton