[ci] Don't skip index-triggered builds (#11915)

This code was there to stop Jenkins restarts from doing a repository scan and scheduling a ton of builds. However, I haven't noticed this happening during restarts lately, and repository scans are useful to patch up PRs that didn't get CI run properly (i.e. while Jenkins was down or something).

For example in #11914 since this code is there all the messed up PRs needed their CI to be manually re-triggered even though they were detected during the scan.

ci/jenkins/Jenkinsfile.j2

@@ -83,14 +83,6 @@ docker_build = 'docker/build.sh'
 max_time = 180
 rebuild_docker_images = false
 
-// skips builds from branch indexing; sourced from https://www.jvt.me/posts/2020/02/23/jenkins-multibranch-skip-branch-index/
-// execute this before anything else, including requesting any time on an agent
-if (currentBuild.getBuildCauses().toString().contains('BranchIndexingCause')) {
-  print "INFO: Build skipped due to trigger being Branch Indexing"
-  currentBuild.result = 'ABORTED' // optional, gives a better hint to the user that it's been skipped, rather than the default which shows it's successful
-  return
-}
-
 // Filenames for stashing between build and test steps
 {% set tvm_runtime = ['build/libtvm_runtime.so', 'build/config.cmake'] %}
 {% set tvm_lib = ['build/libtvm.so'] + tvm_runtime %}