ada: Get rid of Kill_Range_Checks flag on entities

ada: Get rid of Kill_Range_Checks flag on entities

This flag is set in a single context, namely semantic analysis of record
type definitions, to avoid generating spurious range checks from it, and
a large testing campaign showed that, in practice, it makes a difference
in a single case, namely an access-to-constrained-array component with a
default expression, for example:

  type Acc_String is access all String (1 .. 100);

  type Rec (D : Positive) is record
    A : Acc_String := new String (1 .. D);
  end record;

Now there is another mechanism implemented in Process_Range_Expr_In_Decl to
avoid generating spurious range checks, which does not work in this specific
case but can be made to work with a small tweak to Denotes_Discriminant.

gcc/ada/ChangeLog:

	* checks.adb (Range_Checks_Suppressed): Remove test on the
	Kill_Range_Checks flag.
	* einfo.ads (Kill_Range_Checks): Delete.
	* gen_il-fields.ads (Opt_Field_Enum): Remove Kill_Range_Checks.
	* gen_il-gen-gen_entities.adb (Entity_Kind): Likewise.
	* sem_ch3.adb (Record_Type_Declaration): Do not set the
	Kill_Range_Checks flag.
	* sem_util.adb (Denotes_Discriminant): In a default expression,
	also return True for a discriminal.