refactor(conversation-context-bar): slim folder and branch pickers to selection only

- Match popover corner styling of folder picker with branch picker
- Drop 'open folder from disk' entry from folder picker
- Drop 'new branch' entry and dialog from branch picker

src/i18n/messages/pt.json

@@ -1797,9 +1797,6 @@
       "noFolders": "No folders",
       "noBranches": "No branches",
       "noBranch": "(no branch)",
-      "openNewFolder": "Open folder from disk...",
-      "cancel": "Cancel",
-      "create": "Create",
       "commit": "Commit",
       "push": "Push",
       "merge": "Merge",