Remove state and unknown elements

[robander]

Based on discussion at today's TC meeting (June 11 2024), and coming out of the review of "specialization elements" section of elements, we will be removing the following elements from 2.0:

• <state> element -- migration path is to use <data> for 1 to 1 migration if using metadata (both @name and @value are present), OR alternate migration path to use <ph> or <keyword> if using this for content (@value will go into element content in the specialized element)