Remove extension.js file and replace it with dependency from node_modules

[JamesANZ]

Was created because of the following error on bundle:

/Users/jamessangalli/Documents/projects/dot-validator-selector/node_modules/@polkadot/extension-dapp/packageInfo.js:12 path: import.meta && import.meta.url ? new URL(import.meta.url).pathname.substring(0, new URL(import.meta.url).pathname.lastIndexOf('/') + 1) : 'auto', ^ ParseError: Unexpected token