Revert "gnu: cmake: Delete Emacs library."

This reverts commit f037673c31.

gnu/packages/cmake.scm

@@ -85,12 +85,6 @@
            " --exclude-regex ^\\(" (string-join skipped-tests "\\|") "\\)$")))
        #:phases
        (modify-phases %standard-phases
-         (add-after 'unpack 'split-package
-           ;; Remove files that have been packaged in other package recipes.
-           (lambda _
-             (delete-file "Auxiliary/cmake-mode.el")
-             (substitute* "Auxiliary/CMakeLists.txt"
-               ((".*cmake-mode.el.*") ""))))
          (add-before 'configure 'patch-bin-sh
            (lambda _
              ;; Replace "/bin/sh" by the right path in... a lot of