Remove stack processors

For an alternative see scikit-learn's transformers
4 jobs for sphinx-fixes in 2 minutes and 8 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
failed #215523
docker
build_linux_36

failed #215524
docker
build_linux_37

failed #215521
macosx
build_macosx_36

00:02:08

74.0%
failed #215522
macosx
build_macosx_37

00:02:06

74.0%
 
Name Stage Failure
failed
build_linux_37 Build There has been a timeout failure or the job got stuck. Check your timeout limits or try again
No job log
failed
build_linux_36 Build There has been a timeout failure or the job got stuck. Check your timeout limits or try again
No job log
failed
build_macosx_36 Build
WARNING conda_build.build:tests_failed(2896): Tests failed for bob.extension-5.0.2b0-py36h78bea3e_31.conda - moving package to /Users/gitlab/builds/b6d3167a/0/bob/bob.extension/miniconda/conda-bld/broken
TESTS FAILED: bob.extension-5.0.2b0-py36h78bea3e_31.conda
Uploading artifacts for failed job
Uploading artifacts...
Runtime platform
arch=amd64 os=darwin pid=86349 revision=ece86343 version=13.5.0
WARNING: coverage.xml: no matching files
ERROR: No files to upload
Cleaning up file based variables
ERROR: Job failed: exit status 1
failed
build_macosx_37 Build
WARNING conda_build.build:tests_failed(2896): Tests failed for bob.extension-5.0.2b0-py37h78bea3e_31.conda - moving package to /Users/gitlab/builds/b6d3167a/1/bob/bob.extension/miniconda/conda-bld/broken
TESTS FAILED: bob.extension-5.0.2b0-py37h78bea3e_31.conda
Uploading artifacts for failed job
Uploading artifacts...
Runtime platform
arch=amd64 os=darwin pid=86334 revision=ece86343 version=13.5.0
WARNING: coverage.xml: no matching files
ERROR: No files to upload
Cleaning up file based variables
ERROR: Job failed: exit status 1