cleanup DSC references

[ndr-brt]

Feature Request

Currently in the main documentation page there's a paragraph about the difference between EDC and DSC, I think that's not really necessary anymore, especially after the DSP took over
https://github.com/eclipse-edc/docs/tree/main/docs#statement-edc-vs-dsc

Removing that part will make the page shorter and easier to understand

Which Areas Would Be Affected?

e.g., DPF, CI, build, transfer, etc.

Why Is the Feature Desired?

Are there any requirements?

Solution Proposal

If possible, provide a (brief!) solution proposal.