Part 2: Cleanup wording in 5.2.4 Confidential Client

The current wording appears to refer to clause 5.2.3 twice - once by title and once by the numeric reference; I think the second reference was intended to be a reference to part 1 clause 5.2.3, however the reference seems unnecessary given that clause is already included via the reference to the 'Public client' section of Part 2.