It only applied to Windows (not MSVC, like the help said) and the build
was broken with this option. So remove it, as we clearly never test
this.

[ChangeLog][Windows] The -no-rtti configure option was removed, as Qt
5.8 fails to build under that condition. To disable RTTI on user code,
add to your .pro file: CONFIG += rtti_off.

Change-Id: I2bc52f3c7a574209b213fffd149aae1b8d0cf9df
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>