Remove merged params to improve performance

spec/route_handler_spec.cr

@@ -170,8 +170,8 @@ describe "Kemal::RouteHandler" do
     request = HTTP::Request.new(
       "POST",
       "/",
-      body: json_payload.to_json,
-      headers: HTTP::Headers{"Content-Type": "application/json"}
+      body: "_method=DELETE",
+      headers: HTTP::Headers{"Content-Type": "application/x-www-form-urlencoded; charset=UTF-8"}
     )
     io_with_context = create_request_and_return_io(kemal, request)
     client_response = HTTP::Client::Response.from_io(io_with_context, decompress: false)

src/kemal/param_parser.cr

@@ -23,10 +23,6 @@ class Kemal::ParamParser
     parse_request
   end
 
-  def params
-    @query.merge(@body).merge(@json).merge(@url)
-  end
-
   def parse_request
     parse_query
     parse_body

src/kemal/request.cr

@@ -11,7 +11,7 @@ class HTTP::Request
   private def check_for_method_override!
     @override_method = @method
     if @method == "POST"
-      params = Kemal::ParamParser.new(self).params
+      params = Kemal::ParamParser.new(self).body
       if params.has_key?("_method") && HTTP::Request.override_method_valid?(params["_method"])
         @override_method = params["_method"]
       end