chore: remove beta installation instructions from npm (#4560)

Removed instructions for installing the beta release of supabase.

Author: sweatybridge

README.md

@@ -23,12 +23,6 @@ Available via [NPM](https://www.npmjs.com) as dev dependency. To install:
 npm i supabase --save-dev
 ```
 
-To install the beta release channel:
-
-```bash
-npm i supabase@beta --save-dev
-```
-
 When installing with yarn 4, you need to disable experimental fetch with the following nodejs config.
 
 ```