fix: remove redundant/unused permissions (#849)

Addressing review:
#808 (comment)

(We no longer use alarms API and activeTab is superseded by  <all_urls>)

Author: lidel

add-on/manifest.common.json

@@ -14,10 +14,8 @@
   "permissions": [
     "<all_urls>",
     "idle",
-    "activeTab",
     "tabs",
     "notifications",
-    "alarms",
     "storage",
     "unlimitedStorage",
     "contextMenus",