Cleanup SecurityConfiguration

There is some cleanup that can be done in the SecurityConfiguration. I am guessing that much of this probably needs to be cleaned up in the generator rather than just the sample, but at the moment I am pretty swamped so I am submitting this in hopes that someone more familiar can update the generator.

- Clean imports
- Remove unnecessary rememberMeServices() since this is already created via
  classpath scanning
- Remove unnecessary RememberMeAuthenticationProvider. This is already
  created via http.rememberMe().rememberMeServices()
- Remove unnecessary authenticationManager() Bean. This is not necessary
  since the AuthenticationManagerBuilder is being used
- Removed unnecessary UserDetailsService since this is already created via
  classpath scanning
- Use global AuthenticationManagerBuilder to expose to method security