Revert "Enable QtCreator Ios plugin"

This reverts commit 32b7672dd2f7dfa1bd5624c6ce809c882727a998. 
Actually the ios plugin should only be enabled if an ios package/toolchain is installed, too.

Change-Id: I04f1dd06a32282faa6d64f0e9f0d06a82d24a578
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Enable Qt Creator iOS plugin if Qt/iOS installed

Change-Id: Idd0dec9c857da58c3e185727cca2d1311c359fec
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>