Clean out leftovers from test limits

[mfeit-internet2]

This was deprecated and removed; the code for this can come out.

• Remove limit validators from all tests
• Remove limit-is-valid from the PDK.
• Get rid of the files listed below.

./pscheduler-test-trace/misc/trace-limit-passes-test.json
./pscheduler-test-simplestream/misc/simplestream-limit-passes-test.json
./pscheduler-test-rtt/misc/rtt-limit-passes-test.json
./pscheduler-test-dns/misc/dns-limit-passes-test.json