Remove support for generating dotkit files (#11986)

Dotkit is being used only at a few sites and has been deprecated on new
machines. This commit removes all the code that provide support for the
generation of dotkit module files.

A new validator named "deprecatedProperties" has been added to the
jsonschema validators. It permits to prompt a warning message or exit
with an error if a property that has been marked as deprecated is
encountered.

* Removed references to dotkit in the docs
* Removed references to dotkit in setup-env-test.sh
* Added a unit test for the 'deprecatedProperties' schema validator

etc/spack/defaults/config.yaml

@@ -32,7 +32,6 @@ config:
   module_roots:
     tcl:    $spack/share/spack/modules
     lmod:   $spack/share/spack/lmod
-    dotkit: $spack/share/spack/dotkit
 
 
   # Temporary locations Spack can try to use for builds.

etc/spack/defaults/modules.yaml

@@ -16,7 +16,6 @@
 modules:
   enable:
     - tcl
-    - dotkit
   prefix_inspections:
     bin:
       - PATH