tests: Remove old date/time helpers

This is now entirely replaced with GDateTime. Also, drop the related
tests, the two new small helper functions are tested along with the
SPARQL machinery.
5 jobs for wip/carlosg/gdatetime in 2 minutes and 24 seconds
latest
Status Job ID Name Coverage
  Test
passed #1243537
test-alpine-edge

00:01:17

passed #1243538
test-fedora-latest

00:00:57

passed #1243540
test-fedora-rawhide

00:00:57

passed #1243539
test-ubuntu-rolling

00:01:10

 
  Analysis
passed #1243541
coverage-analysis

00:01:06

74.8%