C#: mass-enable diff-informed queries phase 2 - getASelected{Source,Sink}Location() { none() }

[d10c]

Stacks on top of earlier PR: #19659
Uses patch from: https://github.com/github/codeql-patch/pull/88/commits/ec5681e740c18c792443099fb3e413446616a0ee

Adds getASelected{Source,Sink}Location() { none() } override to queries that select a dataflow source or sink as a location, but not both.

[michaelnebel]

AFAICT this LGTM, since the 0'th column (the primary) in the select of the query is the sink and since the source is not used as an additional location (i.e. "$@" substitution).