WEB: remove "String data type" from "Roadmap points pending a PDEP" section.
> pandas is in the process of moving roadmap points to PDEPs (implemented in August 2022). During the transition, some roadmap points will exist as PDEPs, while others will exist as sections below.

This one is now covered by PDEP-14 which has been accepted and therefore no longer pending a PDEP.
I think that point was obsolete for a long time before PDEP-14. Thanks for taking care of this @simonjayhawkins 