content: delete unit-sidebar-details and unused experiments

There are several unused experiments in the templates that have been
fully rolled out and are now deleted.

Change-Id: I603c5e56c24406f718b02e68109b46c347657a75
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/283258
Run-TryBot: Julie Qiu <julie@golang.org>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Trust: Julie Qiu <julie@golang.org>
diff --git a/content/static/html/base.tmpl b/content/static/html/base.tmpl
index 1af51b1..dbed2b0 100644
--- a/content/static/html/base.tmpl
+++ b/content/static/html/base.tmpl
@@ -21,7 +21,7 @@
 <link href="/third_party/dialog-polyfill/dialog-polyfill.css?version={{.AppVersionLabel}}" rel="stylesheet">
 <title>{{if .HTMLTitle}}{{.HTMLTitle}} · {{end}}pkg.go.dev</title>
 {{block "pre_content" .}}{{end}}
-<body class="Site{{if .AllowWideContent}} Site--wide{{end}}{{if (.Experiments.IsActive "unit-page")}} Site--redesign{{end}}">
+<body class="Site{{if .AllowWideContent}} Site--wide{{end}} Site--redesign">
 <header class="Site-header Site-header--dark">
   <div class="Banner">
     <div class="Banner-inner">
@@ -87,11 +87,7 @@
 </aside>
 <div class="NavigationDrawer-scrim js-scrim" role="presentation">
 </div>
-{{if (.Experiments.IsActive "unit-page")}}
-  <div class="Site-content">{{block "main_content" .}}{{end}}</div>
-{{else}}
-  <main class="Site-content">{{block "main_content" .}}{{end}}</main>
-{{end}}
+<div class="Site-content">{{block "main_content" .}}{{end}}</div>
 <footer class="Site-footer">
   {{block "pre_footer" .}}{{end}}
   <div class="Footer">
diff --git a/content/static/html/helpers/_unit_meta.tmpl b/content/static/html/helpers/_unit_meta.tmpl
index 73a8c5c..07d438f 100644
--- a/content/static/html/helpers/_unit_meta.tmpl
+++ b/content/static/html/helpers/_unit_meta.tmpl
@@ -5,9 +5,7 @@
 -->
 
 {{define "unit_meta"}}
-  {{if (.Experiments.IsActive "unit-sidebar-details")}}
-    {{template "unit_meta_details" .}}
-  {{end}}
+  {{template "unit_meta_details" .}}
   <div class="UnitMeta">
     <div class="UnitMeta-header">Repository</div>
     {{if .Details.RepositoryURL}}
diff --git a/content/static/html/pages/search.tmpl b/content/static/html/pages/search.tmpl
index 45bd5c1..a15d8f8 100644
--- a/content/static/html/pages/search.tmpl
+++ b/content/static/html/pages/search.tmpl
@@ -19,11 +19,7 @@
             <img class="SearchResults-emptyContentGopher" src="/static/img/gopher-airplane.svg" alt="The Go Gopher">
             <h3 class="SearchResults-emptyContentMessage">No results found.</h3>
             <p class="SearchResults-emptyContentMessage">
-              {{if (.Experiments.IsActive "frontend-fetch")}}
-                  If you think “{{.Query}}” is a valid package or module, you could try downloading it by visiting <a href="https://pkg.go.dev/{{.Query}}">pkg.go.dev/{{.Query}}</a>.
-              {{else}}
-                  If you think “{{.Query}}” is a valid package, you could try downloading it following the <a href="/about#adding-a-package">instructions here</a>.
-              {{end}}
+              If you think “{{.Query}}” is a valid package or module, you could try downloading it by visiting <a href="https://pkg.go.dev/{{.Query}}">pkg.go.dev/{{.Query}}</a>.
             </p>
           </div>
         {{else}}
diff --git a/internal/experiment.go b/internal/experiment.go
index 7a8de4c..0c0d8c4 100644
--- a/internal/experiment.go
+++ b/internal/experiment.go
@@ -6,15 +6,13 @@
 package internal
 
 const (
-	ExperimentNotAtLatest        = "not-at-latest"
-	ExperimentUnitSidebarDetails = "unit-sidebar-details"
+	ExperimentNotAtLatest = "not-at-latest"
 )
 
 // Experiments represents all of the active experiments in the codebase and
 // a description of each experiment.
 var Experiments = map[string]string{
-	ExperimentNotAtLatest:        "Enable the display of a 'not at latest' badge.",
-	ExperimentUnitSidebarDetails: "Enable the details section in the right sidebar.",
+	ExperimentNotAtLatest: "Enable the display of a 'not at latest' badge.",
 }
 
 // Experiment holds data associated with an experimental feature for frontend