check marks and Xs on front page, tooling support section, need to be updated, right now they look like r code

[MaximMoinat]

The r-block is identical on the index and cdm54 page. Also Codex was stumped why it didn't work and suggested to use html-code directly (✔ and ❗ respectively for the ✔ and ❗).

That said, the table on the index page is duplicated from the cdm54 page.

• Keep: https://ohdsi.github.io/CommonDataModel/cdm54.html#current-support-for-cdm-v5.4
• Remove: https://ohdsi.github.io/CommonDataModel/#current-support-for-cdm-v5.4

I propose to remove the section from the index. @clairblacketer do you agree?