Function remove() should remove mejs container only if it exists

In case of mobile clients (iPad, iPhone and Android) and usage of the
native controls (options iPadUseNativeControls, iPhoneUseNativeControls
and AndroidUseNativeControls) t.container does not exist. In this case
the container may not exist but is implicitly removed in remove().
Merge pull request #1144 from lucash/master

Function remove() should remove mejs container only if it exists