Remove IntelliSense Support for Web

[johnsoncodehk]

Currently we build the web version of VSCode Extension at https://github.com/vuejs/language-tools/blob/master/packages/vscode-vue/scripts/build-browser.js, through vsce publish --target web command to release, this process has some long-standing problems:

• In order to distinguish between the node version and the web version of Extension, we actually need to build 10 environments for node unnecessarily
• This repo always focuses on the behavior of the local IDE, sometimes updates cause problems in the Web IDE and we will not find out and just release it
• Since the web environment cannot dynamically load scripts, providing a web version in a separate extension cannot support the Monoserver feature that we planned

Now Vue's Web support has been integrated into a single extension: https://github.com/volarjs/vscode-typescript-web

We will remove relevant parts from this repo in the next version.