chore: remove unused CSS mask

Author: florianduros

res/css/views/rooms/_E2EIcon.pcss

@@ -59,9 +59,3 @@ Please see LICENSE files in the repository root for full details.
     mask-image: url("$(res)/img/e2e/verified.svg");
     background-color: $e2e-verified-color;
 }
-
-// When using the "normal" icon as a background for verified or warning icon,
-// it should be slightly smaller than the foreground icon
-.mx_E2EIcon_verified, .mx_E2EIcon_warning .mx_E2EIcon_normal::after {
-    mask-size: 90%;
-}