clean: delete wall of text in `wstring.hh`

[shenlebantongying]

I read it, and it provides no value at all. Nobody else should read it again.

We live in a better world now. The problems that the original GD's author was facing are no longer.

For the 4th paragraph about performance, I don't totally agree. (e.g., Temporally converting string to UTF-32 will involves at least one converting + allocation + copying, there could be no performance gains depending on situations.)

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud