Drop support for `jekyll-watch-1.4.0` and older (#7287)

Merge pull request 7287

lib/jekyll/commands/build.rb

@@ -85,16 +85,7 @@ module Jekyll
           end
 
           External.require_with_graceful_fail "jekyll-watch"
-          watch_method = Jekyll::Watcher.method(:watch)
-          if watch_method.parameters.size == 1
-            watch_method.call(
-              options
-            )
-          else
-            watch_method.call(
-              options, site
-            )
-          end
+          Jekyll::Watcher.watch(options, site)
         end
       end
     end