[Web] Drop obsolete sieve filter preset

data/web/inc/presets/sieve/sieve_8.yml

@@ -1,11 +0,0 @@
-headline: lang.sieve_preset_8
-content: |
-  require "envelope";
-  require "variables";
-  if allof (
-    envelope :all :matches "to" "*",
-    not header :contains "To" "${1}",
-    address :is "From" "${1}"
-  ) {
-    discard;
-  }