This removes an obsolete bypass present for long in the predicate
Is_Visible_Component, which is responsible for determining whether
a component present in a private tagged record type is visible in
its extensions.  This bypass would essentially always return true
in bodies of instances, but there is no real basis to do so.

Tested on x86_64-pc-linux-gnu, committed on trunk

2020-06-09  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* sem_ch3.adb (Is_Visible_Component): Do not special-case
	bodies of instances.