Get Rid of nobuild, nolink, and alldeps (#2765)

* Removing the nobuild, nolink, and alldeps dependency types in favor of being explicit.
* This will help with maintenance going forward, as adding more dependency types won't affect existing declared dependencies in weird ways.
* default deptype is still `('build', 'link')`

var/spack/repos/builtin/packages/py-rpy2/package.py

@@ -39,7 +39,7 @@ class PyRpy2(Package):
     version('2.5.6', 'a36e758b633ce6aec6a5f450bfee980f')
 
     extends('python')
-    depends_on('py-six', type=nolink)
+    depends_on('py-six', type=('build', 'run'))
     depends_on('py-setuptools', type='build')
 
     depends_on('R')