[Ada] Remove redundant guard in checks for volatile actuals

[Pierre-Marie de Rodat via Gcc-patches]

When flagging names of volatile objects occurring in actual parameters
we guard against identifiers without entity. This is redundant, because
earlier in the resolution of actual parameters we already guard against
actuals with Any_Type.

Code cleanup related to handling of volatile components; behaviour is
unaffected.

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

gcc/ada/

        * sem_res.adb (Flag_Effectively_Volatile_Objects): Remove
        redundant guard.
diff --git a/gcc/ada/sem_res.adb b/gcc/ada/sem_res.adb
--- a/gcc/ada/sem_res.adb
+++ b/gcc/ada/sem_res.adb
@@ -3868,8 +3868,7 @@ package body Sem_Res is
                when N_Identifier | N_Expanded_Name =>
                   Id := Entity (N);
 
-                  if Present (Id)
-                    and then Is_Object (Id)
+                  if Is_Object (Id)
                     and then Is_Effectively_Volatile_For_Reading (Id)
                     and then
                       not Is_OK_Volatile_Context (Context       => Parent (N),