FIX: Always trust admin and moderators with post edits (#25602)

Removes duplication from LimitedEdit to see who can edit
posts, and also removes the old trust level setting check
since it's no longer necessary.

Also make it so staff can always edit since can_edit_post?
already has a staff escape hatch.

spec/lib/guardian_spec.rb

@@ -1677,25 +1677,31 @@ RSpec.describe Guardian do
         expect(Guardian.new(trust_level_4).can_edit?(post)).to be_truthy
       end
 
-      it "returns false when trying to edit a topic with no trust" do
-        SiteSetting.min_trust_to_edit_post = 2
-        SiteSetting.edit_post_allowed_groups = 12
-        post.user.trust_level = 1
+      it "returns false when trying to edit a topic when the user is not in the allowed groups" do
+        SiteSetting.edit_post_allowed_groups = Group::AUTO_GROUPS[:trust_level_2]
+        post.user.change_trust_level!(TrustLevel[1])
 
         expect(Guardian.new(topic.user).can_edit?(topic)).to be_falsey
       end
 
-      it "returns false when trying to edit a post with no trust" do
-        SiteSetting.min_trust_to_edit_post = 2
-        SiteSetting.edit_post_allowed_groups = 12
-        post.user.trust_level = 1
+      it "returns false when trying to edit a post when the user is not in the allowed groups" do
+        SiteSetting.edit_post_allowed_groups = Group::AUTO_GROUPS[:trust_level_2]
+        post.user.change_trust_level!(TrustLevel[1])
 
         expect(Guardian.new(post.user).can_edit?(post)).to be_falsey
       end
 
-      it "returns true when trying to edit a post with trust" do
-        SiteSetting.min_trust_to_edit_post = 1
-        post.user.trust_level = 1
+      it "returns true when editing a post when the user is in the allowed groups" do
+        SiteSetting.edit_post_allowed_groups = Group::AUTO_GROUPS[:trust_level_1]
+        post.user.change_trust_level!(TrustLevel[1])
+
+        expect(Guardian.new(post.user).can_edit?(post)).to be_truthy
+      end
+
+      it "returns true when editing a post when the user is admin regardless of groups" do
+        SiteSetting.edit_post_allowed_groups = Group::AUTO_GROUPS[:trust_level_2]
+        post.user.update!(admin: true)
+        post.user.change_trust_level!(TrustLevel[1])
 
         expect(Guardian.new(post.user).can_edit?(post)).to be_truthy
       end