cleanup locale function usage (#27227) (#27240)

Backport #27227 by @denyskon

Throughout the Gitea codebase, you can meet some weird constructions to
make `locale.Tr` work in subtemplates.
Since we now have `ctx.Locale.Tr` which solves that problem, clean up
various templates which pass `locale` through `dict` or use some weird
constructions like `$.root.locale`

Going on, it would be great to replace every case of `$.locale.Tr` and
`.locale.Tr` with `ctx.Locale.Tr`, but that needs to be done with
patience.

Co-authored-by: Denys Konovalov <kontakt@denyskon.de>

templates/repo/issue/search.tmpl

@@ -7,7 +7,7 @@
 		<input type="hidden" name="project" value="{{$.ProjectID}}">
 		<input type="hidden" name="assignee" value="{{$.AssigneeID}}">
 		<input type="hidden" name="poster" value="{{$.PosterID}}">
-		{{template "shared/searchinput" dict "locale" .locale "Value" .Keyword}}
+		{{template "shared/searchinput" dict "Value" .Keyword}}
 		{{if .PageIsIssueList}}
 			<button id="issue-list-quick-goto" class="ui small icon button gt-hidden" data-tooltip-content="{{.locale.Tr "explore.go_to"}}" data-repo-link="{{.RepoLink}}">{{svg "octicon-hash"}}</button>
 		{{end}}