Clean up change-list columns

The COMMENTS column and the STATUS column are obsolete by introducing
the submit requirements column.

The COMMENTS column could just be removed, no complexity involved.

Replacing the STATUS column by the new STATUS2 column was a bit
trickier, because there was some magic replacing in place. We have
moved the canonical rewriting of configured columns into user-model,
so this is easier to consume by components.

Columns are not enabled anymore based on the server config or flags,
so this logic could be simplified a bit.

Refactored `computeIsColumnHidden()` to only take one argument. The
second was always `this.visibleChangeTableColumns`, so no need to pass
that in.

Tried using the `ColumnNames` enum in a few more places instead of
using strings.

Release-Notes: skip
Google-Bug-Id: b/297159286
Change-Id: I2e42743365d332851a666c56e07fd69c03c28d7f
diff --git a/polygerrit-ui/app/constants/constants.ts b/polygerrit-ui/app/constants/constants.ts
index 25d25b0..d28f33f 100644
--- a/polygerrit-ui/app/constants/constants.ts
+++ b/polygerrit-ui/app/constants/constants.ts
@@ -94,16 +94,13 @@
 
 export enum ColumnNames {
   SUBJECT = 'Subject',
-  // TODO(milutin) - remove once Submit Requirements are rolled out.
-  STATUS = 'Status',
   OWNER = 'Owner',
   REVIEWERS = 'Reviewers',
-  COMMENTS = 'Comments',
   REPO = 'Repo',
   BRANCH = 'Branch',
   UPDATED = 'Updated',
   SIZE = 'Size',
-  STATUS2 = ' Status ', // spaces to differentiate from old 'Status'
+  STATUS = 'Status',
 }
 
 /**