gh-13114: Remove 'slots filled' message in tab context (gh-13102)

Author: Panemiko

locales/en-US/browser/browser/zen-general.ftl

@@ -15,7 +15,7 @@ tab-context-zen-reset-pinned-tab =
 tab-context-zen-add-essential =
     .label = Add to Essentials
     .accesskey = E
-tab-context-zen-add-essential-badge = { $num } / { $max } slots filled
+tab-context-zen-add-essential-badge = { $num } / { $max }
 tab-context-zen-remove-essential =
     .label = Remove from Essentials
     .accesskey = R