Remove Apache 2.0 license mentions in 'deb', make consistent with 'rpm'

[arm4b]

To avoid any confusion, remove Apache 2.0 license from our deb enterprise packages. Additionally, it adds consistency with rpm which doesn't mention any Apache2.0.

Other similar changes:

• https://github.com/StackStorm/bwc-enterprise-packages/pull/30
• https://github.com/StackStorm/st2-enterprise-auth-backend-ldap/pull/57
• https://github.com/StackStorm/st2flow/pull/341
• https://github.com/StackStorm/bwc-ui/pull/67
• https://github.com/StackStorm/st2-enterprise-rbac-backend/