Old post I know, but if anyone needs a method other than the built in delete edge/vertex, select all the vertices in the mesh you are trying to target, then:

selected = cmds.ls(sl=1, fl=1)

cmds.select(clear=True)
for v in selected:
if len(cmds.polyInfo(v,ve=True)[0].split(" ")) == 4:
cmds.select(v,add=True)

cmds.delete(cmds.ls(sl=True))