Remove border styling from iframe

Removed border styling from iframe in Mach-Zehnder Interferometer documentation.

Author: beniroquai

docs/usage/disc/holobox/03_MachZehnderInterferometer/03_mach-zehnder_interferometer.md

@@ -37,7 +37,6 @@ The QBox is a collaboration between openUC2 and OQ3
   width="100%"
   height="500"
   frameborder="0"
-  style="border-radius: 8px; border: 1px solid #ddd;"
 ></iframe>
 </div>