Remove diff chain example from documentation to fix wiki

[cycraig]

Description of change

Removes the reference to the diff_chain example from the documentation, which removed in #759. This is causing the wiki to break.

Module not found: Error: Can't resolve './../../../bindings/wasm/examples/src/diff_chain.js' in 'C:\Work\iota\identity.rs\documentation\local-wiki\iota-wiki\external\identity.rs\documentation\docs\advanced'
Module not found: Error: Can't resolve './../../../examples/low-level-api/diff_chain.rs' in 'C:\Work\iota\identity.rs\documentation\local-wiki\iota-wiki\external\identity.rs\documentation\docs\advanced'
client (webpack 5.69.1) compiled with 2 errors and 1 warning

Type of change

• Bug fix (a non-breaking change which fixes an issue)
• Enhancement (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Fix

How the change has been tested

The documentation runs without error now: npm run setup && npm run start

Change checklist

• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes