Remove check-scudo from buildbot_cmake.

check-scudo is deleted as of https://reviews.llvm.org/D138157. I did a
quick 'git grep -i scudo', and this was all the references I found.

The sanitizer-ppc64le-linux bot is failing as well, but I'm not exactly
sure where that buildscript comes from. I don't think it's from here,
otherwise the build steps would have included an 'in gcc build' suffix.