iwlwifi: mvm: Remove antenna c references

Since antenna c is not in use and won't be relevant after the new rate &
flags, remove all it's references

Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20211017113927.5e39106ec75b.I4281edc844f734bf9591396a5cc8009ad37ccda8@changeid


Signed-off-by: Luca Coelho <luciano.coelho@intel.com>