Migrate unit test YANG inputs

We have a number of small yang files used in unit tests. YANGTOOLS-1483 introduces utilities which allow us to inline them into tests themselves using text blocks.

Migrate all files found by

 $ find . -name \*.yang | fgrep src/test/resources | sort | fgrep -v ./parser/ | xargs -n 1 wc -l 

and reporting the number of lines less than, or equal to, 50.