chore: Remove framework demos.

[gonfunko]

The basics

• I validated my changes

The details

Resolves

Fixes #1679
Obsoletes #2589, #609, #282, #842

Proposed Changes

This PR removes the demos of using Blockly with various web frameworks.

Reason for Changes

During a team discussion, we decided to remove these because:

• Our team does not have a level of familiarity with these frameworks and their evolving best practices or the time to invest in keeping them up to date as effective demos, causing them to be perpetually outdated
• The demos generally illustrated very little, mostly just loading Blockly onto a page rendered by the framework
• Prompting your choice of LLM to "Create a $FRAMEWORK web app that uses Blockly to display a block code editor" is likely to provide a much more up to date example for bootstrapping a new project.