remove dependence on clangdev on linux

this does not seem necessary to build, and prevents us from letting `clangxx`
depend on `libcxx-devel` (because it would create a build cycle); see
conda-forge/clangdev-feedstock#315 (comment)

recipe/meta.yaml

@@ -39,7 +39,7 @@ requirements:
     - {{ stdlib('c') }}
     - python >3               # [not osx]
   host:
-    - clangdev {{ version }}  # [not osx]
+    # - clangdev {{ version }}  # [not osx]
     - llvmdev {{ version }}   # [not osx]
 
 outputs: