Remove py-cantera dependency - not available in Spack builtin repo

py-cantera doesn't exist in Spack's builtin repository, causing
'mfc is unsatisfiable' error. Removing for now; will add back
when chemistry variant is implemented and py-cantera is available.

Author: sbryngelson

packaging/spack/SPACK.md

@@ -94,7 +94,6 @@ Build-time dependencies (required during compilation):
 - [email protected] or newer - Build system
 - py-fypp - Fortran preprocessor
 - [email protected] or newer - Build scripts
-- [email protected] or newer - Chemistry library (for future chemistry support)
 
 Runtime dependencies (always required):
 - [email protected] or newer - Fast Fourier Transform library

packaging/spack/package.py

@@ -41,7 +41,8 @@ class Mfc(CMakePackage):
     depends_on("[email protected]:", type="build")
     depends_on("py-fypp", type="build")
     depends_on("python@3:", type="build")
-    depends_on("py-cantera@3:", type="build")
+    # Note: py-cantera is not yet available in Spack builtin repo
+    # Will add when chemistry variant is implemented
 
     # Runtime dependencies
     depends_on("fftw@3:", when="~mpi")