Revert "FEATURE: hidden site setting to disable search prefix matching (#20058)" (#20073)

This reverts commit 64f7b97d08.

Too many side effects for this setting, we have decided to remove it

spec/lib/search_spec.rb

@@ -2580,25 +2580,4 @@ RSpec.describe Search do
       expect(result.categories.length).to eq(0)
     end
   end
-
-  context "when enable_search_prefix_matching is disabled" do
-    before do
-      SearchIndexer.enable
-      SiteSetting.enable_search_prefix_matching = false
-    end
-
-    fab!(:post) do
-      Fabricate(:post, topic: topic, raw: "this body of the post contains abracadabra")
-    end
-
-    it "omits prefix search results" do
-      SearchIndexer.index(post, force: true)
-
-      result = Search.execute("abra")
-      expect(result.posts.length).to eq(0)
-
-      result = Search.execute("abracadabra")
-      expect(result.posts.length).to eq(1)
-    end
-  end
 end