Revert increased width on pull pages (#21470)

- Revert a behavior from #21012, which liberally added `fluid padded` to
non-split style pull pages, this caused it to take up the whole
screen(such in split-style pull pages) on pull pages where the diff was
shown.
- Resolves #21460


### Before

![image](https://user-images.githubusercontent.com/25481501/196005545-bb8370c1-330d-4d47-be52-6d0c93e61583.png)

![image](https://user-images.githubusercontent.com/25481501/196005546-0022198e-6ef7-45d1-958c-77a042e5f80b.png)

### After

![image](https://user-images.githubusercontent.com/25481501/196005572-76a38309-9a41-412a-854f-24eae2b9ae4f.png)

![image](https://user-images.githubusercontent.com/25481501/196005551-2495b93d-ad08-4f59-abba-c327dadcc915.png)

templates/repo/pulls/files.tmpl

@@ -5,7 +5,7 @@
 
 <div class="page-content repository view issue pull files diff">
 	{{template "repo/header" .}}
-	<div class="ui container fluid padded">
+	<div class="ui container {{if .IsSplitStyle}}fluid padded{{end}}">
 		<div class="navbar">
 			{{template "repo/issue/navbar" .}}
 			<div class="ui right">