[release/2.0] Move documentation from readthedocs to Wiki (#1855)

* Remove readthedocs documentation

Author: climbfuji

.gitmodules

@@ -2,10 +2,6 @@
   path = spack
   url = https://github.com/jcsda/spack
   branch = release/2.0
-[submodule "doc/CMakeModules"]
-  path = doc/CMakeModules
-  url = https://github.com/noaa-emc/cmakemodules
-  branch = v1.3.0
 [submodule "repos/builtin"]
   path = repos/builtin
   url = https://github.com/jcsda/spack-packages