Refactor repo unit "disabled" check (#31389)

1. There are already global "unit consts", no need to use context data, which is fragile
2. Remove the "String()" method from "unit", it would only cause rendering problems in templates

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Co-authored-by: silverwind <me@silverwind.io>

templates/repo/issue/view_content/comments.tmpl

@@ -574,7 +574,6 @@
 				{{template "repo/commits_list_small" dict "comment" . "root" $}}
 			{{end}}
 		{{else if eq .Type 30}}
-			{{if not $.UnitProjectsGlobalDisabled}}
 			<div class="timeline-item event" id="{{.HashTag}}">
 				<span class="badge">{{svg "octicon-project"}}</span>
 				{{template "shared/user/avatarlink" dict "user" .Poster}}
@@ -599,7 +598,6 @@
 					{{end}}
 				</span>
 			</div>
-			{{end}}
 		{{else if eq .Type 32}}
 			<div class="timeline-item-group">
 				<div class="timeline-item event" id="{{.HashTag}}">

templates/repo/issue/view_content/context_menu.tmpl

@@ -15,7 +15,7 @@
 			{{if not .ctxData.Repository.IsArchived}}
 				{{$needDivider = true}}
 				<div class="item context js-aria-clickable quote-reply {{if .diff}}quote-reply-diff{{end}}" data-target="{{.item.HashTag}}-raw">{{ctx.Locale.Tr "repo.issues.context.quote_reply"}}</div>
-				{{if not .ctxData.UnitIssuesGlobalDisabled}}
+				{{if not ctx.Consts.RepoUnitTypeIssues.UnitGlobalDisabled}}
 					<div class="item context js-aria-clickable reference-issue" data-target="{{.item.HashTag}}-raw" data-modal="#reference-issue-modal" data-poster="{{.item.Poster.GetDisplayName}}" data-poster-username="{{.item.Poster.Name}}" data-reference="{{$referenceUrl}}">{{ctx.Locale.Tr "repo.issues.context.reference_issue"}}</div>
 				{{end}}
 				{{if or .ctxData.Permission.IsAdmin .IsCommentPoster .ctxData.HasIssuesOrPullsWritePermission}}