[lldb][NFCI] Remove use of ConstString from FilterRule in StructuredDataDarwinLog (#68347)

There are only ever 2 FilterRules and their operations are either
"regex" or "match". This does not benefit from deduplication since the
strings have static lifetime and we can just compare StringRefs pointing
to them. This is also not on a fast path, so it doesn't really benefit
from the pointer comparisons of ConstStrings.