Fix Performance/DeletePrefix cop (#24796)

app/services/activitypub/fetch_remote_actor_service.rb

@@ -67,7 +67,7 @@ class ActivityPub::FetchRemoteActorService < BaseService
   end
 
   def split_acct(acct)
-    acct.gsub(/\Aacct:/, '').split('@')
+    acct.delete_prefix('acct:').split('@')
   end
 
   def supported_context?

app/services/resolve_account_service.rb

@@ -100,7 +100,7 @@ class ResolveAccountService < BaseService
   end
 
   def split_acct(acct)
-    acct.gsub(/\Aacct:/, '').split('@')
+    acct.delete_prefix('acct:').split('@')
   end
 
   def fetch_account!

app/services/tag_search_service.rb

@@ -2,7 +2,7 @@
 
 class TagSearchService < BaseService
   def call(query, options = {})
-    @query   = query.strip.gsub(/\A#/, '')
+    @query   = query.strip.delete_prefix('#')
     @offset  = options.delete(:offset).to_i
     @limit   = options.delete(:limit).to_i
     @options = options