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/user/dashboard/issues.tmpl

@@ -77,7 +77,7 @@
 							<input type="hidden" name="repos" value="[{{range $.RepoIDs}}{{.}},{{end}}]">
 							<input type="hidden" name="sort" value="{{$.SortType}}">
 							<input type="hidden" name="state" value="{{$.State}}">
-							{{template "shared/searchinput" dict "locale" .locale "Value" $.Keyword}}
+							{{template "shared/searchinput" dict "Value" $.Keyword}}
 							<button id="issue-list-quick-goto" class="ui small icon button gt-hidden" data-tooltip-content="{{.locale.Tr "explore.go_to"}}">{{svg "octicon-hash"}}</button>
 							<button class="ui small icon button" aria-label="{{.locale.Tr "explore.search"}}">{{svg "octicon-search"}}</button>
 						</div>

templates/user/dashboard/milestones.tmpl

@@ -51,7 +51,7 @@
 							<input type="hidden" name="repos" value="[{{range $.RepoIDs}}{{.}},{{end}}]">
 							<input type="hidden" name="sort" value="{{$.SortType}}">
 							<input type="hidden" name="state" value="{{$.State}}">
-							{{template "shared/searchinput" dict "locale" .locale "Value" $.Keyword}}
+							{{template "shared/searchinput" dict "Value" $.Keyword}}
 							<button class="ui small icon button" type="submit" aria-label="{{.locale.Tr "explore.search"}}">{{svg "octicon-search"}}</button>
 						</div>
 					</form>