Remove explicit setting of the compiler

This change was tested with cable @git.215-additional-cmake-changes.

packages/cable/package.py

@@ -25,7 +25,7 @@ def url_for_version(self, version):
 
     variant(
         "mpi",
-        default=False,
+        default=True,
         description="Build MPI executable.",
     )
     variant(
@@ -41,19 +41,5 @@ def url_for_version(self, version):
     def cmake_args(self):
         args = []
         if self.spec.satisfies("+mpi"):
-            args += [
-                self.define_from_variant("CABLE_MPI", "mpi"),
-                # TODO(Sean): we should let CMake find the MPI compiler instead
-                # of specifying it explicitly. However, this requires adding
-                # find_package(MPI) to the CMakeLists.txt file. This was not
-                # done in https://github.com/CABLE-LSM/CABLE/pull/200 so that
-                # we can demonstrate binary equivalence in the executables when
-                # transitioning from a Makefile based to a CMake based build
-                # system. Once find_package(MPI) is added, this file should be
-                # updated.
-                self.define(
-                    "CMAKE_Fortran_COMPILER",
-                    self.spec["mpi"].mpifc,
-                ),
-            ]
+            args.append(self.define_from_variant("CABLE_MPI", "mpi"))
         return args