get rid of Q_*_EXPORT_INLINE macros

get rid of Q_*_EXPORT_INLINE macros

> Girish:
> We should be able to remove the macro completely today,
> just mark all those functions as plain inline.
> With Qt5, we don't have to worry about bc yet.

this fixes "import attribute ignored" warnings on mingw with -fno-keep-inline-dllexport

Change-Id: I616e5de7c8d59953ce03a316b941a439fae56298
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>