remove platform=cray (#43796)

Remove support for `cray` as a separate platform.

Any platform previously detected as `cray` is now detected as `linux`.

Users who still need platform=cray have to stick to Spack 0.22

etc/spack/defaults/cray/modules.yaml

@@ -1,16 +0,0 @@
-# -------------------------------------------------------------------------
-# This is the default configuration for Spack's module file generation.
-#
-# Settings here are versioned with Spack and are intended to provide
-# sensible defaults out of the box. Spack maintainers should edit this
-# file to keep it current.
-#
-# Users can override these settings by editing the following files.
-#
-# Per-spack-instance settings (overrides defaults):
-#   $SPACK_ROOT/etc/spack/modules.yaml
-#
-# Per-user settings (overrides default and site settings):
-#   ~/.spack/modules.yaml
-# -------------------------------------------------------------------------
-modules: {}