Do not export the SuiteSparse Partition target

The Partition target merely signals that CHOLMOD was compiled with METIS
and adds nothing beyond CHOLMOD and METIS. Exporting it as a dependency
of Ceres forced consumers to repeat the partitioning check in their own
environment. If the check failed there, the Ceres target referred to a
missing target and CMake generation failed.

Link CHOLMOD and METIS directly and use the Partition component only to
enable CHOLMOD partitioning.

Fixes #1172

Change-Id: If9ea17dd462f3712e92039c0c0217545ba2ea57e

internal/ceres/CMakeLists.txt

diff --git a/internal/ceres/CMakeLists.txt b/internal/ceres/CMakeLists.txt
index e541e76..9a20047 100644
--- a/internal/ceres/CMakeLists.txt
+++ b/internal/ceres/CMakeLists.txt
@@ -100,10 +100,9 @@
   add_definitions(-DCERES_SUITESPARSE_VERSION="${SuiteSparse_VERSION}")
   list(APPEND CERES_LIBRARY_PRIVATE_DEPENDENCIES SuiteSparse::CHOLMOD
     SuiteSparse::SPQR)
-
-  if (SuiteSparse_Partition_FOUND)
-    list(APPEND CERES_LIBRARY_PRIVATE_DEPENDENCIES SuiteSparse::Partition)
-  endif (SuiteSparse_Partition_FOUND)
+  # SuiteSparse::Partition only signals METIS support in CHOLMOD. Linking it
+  # would make consumers depend on the partitioning check succeeding in their
+  # environment. CHOLMOD and METIS are linked explicitly instead.
 endif (_Ceres_FEATURE_SUITESPARSE)
 
 if (_Ceres_FEATURE_CHOLMOD_PARTITION OR _Ceres_FEATURE_EIGEN_METIS)