UI: Remove m3u8 format from simple output mode

This option regularly confuses users, who accidentally select it and
then ask why they have hundreds of 2-4 second video clips in their
output folder. HLS output format to file is a pretty niche use case,
so let's keep it in advanced mode only.

UI/forms/OBSBasicSettings.ui

@@ -1769,11 +1769,6 @@
                         <string notr="true">ts</string>
                        </property>
                       </item>
-                      <item>
-                       <property name="text">
-                        <string notr="true">m3u8</string>
-                       </property>
-                      </item>
                      </widget>
                     </item>
                     <item row="4" column="0">