[Development] Dropping qtserialbus from Qt 5.6 -- it doesn't compile in C++98

[Welbourne Edward]

> Why do we insist on testing for something that proxies the real need?
> We need X and we know that Y provides X, so we test for Y. Why can't
> we just test for X?

Indeed.  It reminds me of the web-sites that used to test with a few
browsers and refuse access to anything but the known-good versions of
those browsers - even if the untested browser works just fine.  It
pointlessly limits use and pressures folk into using one of the few
things you've taken the trouble to test with; this marginalises new
entrants in the market by punishing their customers for daring to try
something new.

Likewise for compilers: you want a particular feature, so test for that.
Don't oblige your users to chose from among the few compilers you can
spare the time to test, version-by-version.  Better yet, when the
compiler supplier introduces a regression that breaks support for some
feature, the test automatically detects the problem in a version you
never had a chance to check because it's been released since you
released your code.

	Eddy.