Remove incorrect license information from README.md

No other Qt module has a README.md, therefore anything put here
has a high risk of going stale. Rather use the official documentation
for license information.

Task-number: QTBUG-64135
Change-Id: I0b233ee9f648f514cedf3ea0b152518fff915d16
Reviewed-by: Jani Heikkinen <jani.heikkinen@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

README.md

@@ -32,6 +32,3 @@ To use, add `websockets` to the QT variable.
 
 ### Missing Features
 * Extensions and sub-protocols
-
-### License
-This code is licensed under LGPLv3 or LGPLv2.1.