DDSXTY14 — Update Section 6.1 and 7.2.1

Section 6.1 was written as a motivation for XTYPES and contains a few misleading statements that are no longer true once XTYPES was adopted. E.g. that DDS needs to be used withg staically-defined types.

Also there is information there that has not been updated to match the more recent versions of XTYPES and is now confusing at best. For example Table 2 mentions CDR and Parameterized CDR and never mentions XCDR or the versions of XCDR.

This section should be reviwed and updated.

7.2.1 Background (Non-Normative)
says:
The specified type system is designed to be sufficiently rich to encompass the needs of modern distributed applications and cover the basic data types available both in common programming languages such as C/C++, Java, and C#, as well as in distributed computing data-definition languages such as IDL or XDR.

XDR is far from modern. It should be replaced with nore modern formats like Protobuf or Avro