This reverts commit 893e4ed0dd.
This caused regressions in existing elements which override/set things
like QoS and such in their own init functions. If the base class does
this in ::constructed() now it will override the subclass settings
again with its own, which can have unintended side-effects.
Case in point is gdkpixbufsink which disabled QoS there, and this
patch would reliably make the unit test fail in valgrind because
now frames are dropped because of QoS (when QoS should really be
disabled).
Fixes#2794
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5006>