The hack to use the environment variable for turning off the
mouse cursor is broken when running against Ministro, because
Ministro does not pass the environment on.

A better solution is to make it possible to turn the cursor
in the EGLFS plugin off in the hooks instead.

Task-number: QTBUG-30553
Change-Id: Id09b48c350d2c95de9bb174f7480cf0cd2bf8145
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>