redis: Get rid of unused (and unhelpful) module parameters

• Get rid of 'package', 'package_version', 'service_name' and 'config_template' arguments -- they were all unused.
• Don't alias 'redis-server' to 'redis' -- it just adds misdirection.
• Get rid of OS guards in redis module. The module is WMF-specific and not likely to be reusable by third parties, so there's no need to assert that the OS is Ubuntu or Debian.

Change-Id: I4e6a7fbb2b98d8f01d6ad02c4d4a5e631f3af320