Always go full width in PR view (#22844)

This is an alternative solution to #22824 
and would also close #22781

This makes the PR diff view always full width.
It makes sense to make use of that screen real estate. If you want a
more narrow view you can always resize your browser.
It also avoids cluttering the UI with another button + the database with
another column for the setting.

This is also how github and gitlab do it.

templates/repo/commit_page.tmpl

@@ -1,7 +1,7 @@
 {{template "base/head" .}}
 <div role="main" aria-label="{{.Title}}" class="page-content repository diff">
 	{{template "repo/header" .}}
-	<div class="ui container {{if .IsSplitStyle}}fluid padded{{end}}">
+	<div class="ui container fluid padded">
 		{{$class := ""}}
 		{{if .Commit.Signature}}
 			{{$class = (printf "%s%s" $class " isSigned")}}

templates/repo/diff/compare.tmpl

@@ -1,7 +1,7 @@
 {{template "base/head" .}}
 <div role="main" aria-label="{{.Title}}" class="page-content repository diff {{if .PageIsComparePull}}compare pull{{end}}">
 	{{template "repo/header" .}}
-	<div class="ui container {{if .IsSplitStyle}}fluid padded{{end}}">
+	<div class="ui container fluid padded">
 
 	<h2 class="ui header">
 		{{if and $.PageIsComparePull $.IsSigned (not .Repository.IsArchived)}}

templates/repo/pulls/files.tmpl

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