[Ada] Do not systematically suppress checks on atree.adb

[Pierre-Marie de Rodat]

This does not make a significant enough performance difference.

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

gcc/ada/

        * atree.adb: Do not suppress checks.
diff --git a/gcc/ada/atree.adb b/gcc/ada/atree.adb
--- a/gcc/ada/atree.adb
+++ b/gcc/ada/atree.adb
@@ -27,12 +27,11 @@
 --  file must be properly reflected in the file atree.h which is a C header
 --  file containing equivalent definitions for use by gigi.
 
---  Checks and assertions in this package are too slow, and are mostly needed
---  when working on this package itself, or on gen_il, so we disable them.
+--  Assertions in this package are too slow, and are mostly needed when working
+--  on this package itself, or on gen_il, so we disable them.
 --  To debug low-level bugs in this area, comment out the following pragmas,
 --  and run with -gnatd_v.
 
-pragma Suppress (All_Checks);
 pragma Assertion_Policy (Ignore);
 
 with Aspects;        use Aspects;