ci: Drop clang and unit tests from here

We're running them in Prow now and we're hitting capacity
issues in CentOS CI.  Bigger picture, the "just build and unit test"
stuff runs in any cluster, so let's save our bare metal capacity
for our compose/VM testing.

.cci.jenkinsfile

@@ -22,24 +22,6 @@ codestyle: {
         ci/commit-validation.sh
       """)
   }
-},
-unit: {
-  // this branch runs unit tests (both Rust-based and C-based)
-  def n = 5
-  cosaPod(buildroot: true, runAsUser: 0, memory: "2Gi", cpu: "${n}") {
-      checkout scm
-      shwrap("""
-        MAKE_JOBS=${n} CARGO_BUILD_JOBS=${n} ci/unit.sh
-      """)
-  }
-},
-clang: {
-  // Build with clang/clang++
-  def n = 5
-  cosaPod(buildroot: true, runAsUser: 0, memory: "2Gi", cpu: "${n}") {
-      checkout scm
-      shwrap("MAKE_JOBS=${n} ci/clang-build-check.sh")
-  }
 }
 }