Remove ONLY_SHOW_RELEVANT_REPOS setting (#21962)

Every user can already disable the filter manually, so the explicit
setting is absolutely useless and only complicates the logic.

Previously, there was also unexpected behavior when multiple query
parameters were present.

---------

Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

models/repo/repo_list.go

@@ -494,7 +494,7 @@ func SearchRepositoryCondition(opts *SearchRepoOptions) builder.Cond {
 	}
 
 	if opts.OnlyShowRelevant {
-		// Only show a repo that either has a topic or description.
+		// Only show a repo that has at least a topic, an icon, or a description
 		subQueryCond := builder.NewCond()
 
 		// Topic checking. Topics are present.
@@ -504,13 +504,13 @@ func SearchRepositoryCondition(opts *SearchRepoOptions) builder.Cond {
 			subQueryCond = subQueryCond.Or(builder.And(builder.Neq{"topics": "null"}, builder.Neq{"topics": "[]"}))
 		}
 
-		// Description checking. Description not empty.
+		// Description checking. Description not empty
 		subQueryCond = subQueryCond.Or(builder.Neq{"description": ""})
 
-		// Repo has a avatar.
+		// Repo has a avatar
 		subQueryCond = subQueryCond.Or(builder.Neq{"avatar": ""})
 
-		// Always hide repo's that are empty.
+		// Always hide repo's that are empty
 		subQueryCond = subQueryCond.And(builder.Eq{"is_empty": false})
 
 		cond = cond.And(subQueryCond)