Effect: Fix a unnecessary conditional statement in .stop()

Because of the above conditional, the 'type' variable has a value of type
'string' or undefined. Therefore, boolean comparisons for 'type' variable
is always unnecessary because it return true. The patch removed the
unnecessary conditional statement.

Fixes gh-4374
Closes gh-4375

(cherry picked from commit 110802c)

src/effects.js

@@ -542,7 +542,7 @@ jQuery.fn.extend( {
 			clearQueue = type;
 			type = undefined;
 		}
-		if ( clearQueue && type !== false ) {
+		if ( clearQueue ) {
 			this.queue( type || "fx", [] );
 		}