QtIFW

Fix code examples to use 'MaintenanceToolName'

Commit 27390528bd renamed the <UninstallerName> tag to
<MaintenanceToolName>. Fix remaining uses of <UninstallerName> to
use the new tag.

Change-Id: I2a397b7c23e2d3a0e8d8759f24d407cdfd4e5fa5
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@theqtcompany.com>