Remove explicit cutting decompositions in favor of using the KAK decomposition everywhere

[garrison]

Currently, our code has explicit cutting decompositions of most standard gates. These decompositions were developed before we had general code that uses the KAK decomposition. So far, we have continued to use these decompositions even though we have general code because sometimes the KAK decomposition returned by Qiskit has unnecessary single-qubit unitaries. I just learned that there is a Qiskit issue tracking this: Qiskit/qiskit#9315. Once this is fixed, we could potentially remove the explicit cutting decompositions and use the KAK decomposition for everything.