openfoam-com package: build without kahip by default (#11259)

Kahip does not build with clang (conflicts('%clang') in kahip package.
Because of this, openfoam-com %clang fails concretization. Therefore,
this changes the default openfoam-com variant for kahip to False.

var/spack/repos/builtin/packages/openfoam-com/package.py

@@ -276,7 +276,7 @@ class OpenfoamCom(Package):
             description='With 64-bit labels')
     variant('knl', default=False,
             description='Use KNL compiler settings')
-    variant('kahip', default=True,
+    variant('kahip', default=False,
             description='With kahip decomposition')
     variant('metis', default=False,
             description='With metis decomposition')