remove Criterion submodule

remove Criterion submodule

Criterion is a testing framework that has been used for writing Graphviz unit
tests in the past (see tests/unit_tests). These unit tests are not currently
enabled. However, Windows CI unconditionally checks out all submodules, thus
pulling in a version of Criterion that goes unused.

This change removes the previously described behavior. If/when the
Criterion-based unit tests are resurrected, an up to date version of Criterion
can be pulled in via a package manager or the Windows build dependencies
repository¹ instead.

This change should slightly accelerate Windows CI jobs.

¹ https://gitlab.com/graphviz/graphviz-build-utilities