Nav Unification: Cleanup code after feature is fully released to 100% of users

[cpapazoglou]

After this feature is released to 100% of the users, we should cleanup any feature flags and place the code appropriately. Generally a search for config.isEnabled( 'nav-unification' ) should be enough to indicate what needs to be removed.

• wp-calypso/client/my-sites/sidebar-unified/style.scss

  Line 1 in 39acb06

  // The following changes should be merged in their respective files before nav unification goes to production

• wp-calypso/client/assets/stylesheets/_nav-unification.scss

  Line 1 in 99784ab

  /* stylelint-disable selector-max-id */

• wp-calypso/client/components/sidebar-navigation/index.jsx

  Line 23 in 9bdafa7

  if ( config.isEnabled( 'nav-unification' ) ) {

• After a period of time (that of which is unknown) the nav unification announcement modal will likely need to be cleaned up.

[tjcafferkey]

On hold until Nav Unification is active on Jetpack sites.