[Ada] Fix small discrepancy between -gnatG and -gnatD[G] outputs

gcc/ada/

	* sprint.ads (Source_Dump): Fix typo in comment.
	* sprint.adb (Source_Dump): Set Dump_Freeze_Null for both -gnatG
	and -gnatD.
	* switch-c.adb (Scan_Front_End_Switches) <'D'>: Remove obsolete
	kludge.

gcc/ada/sprint.adb

@@ -588,7 +588,7 @@ package body Sprint is
                              Print_Generated_Code or
                              Debug_Generated_Code;
       Dump_Original_Only  := Debug_Flag_O;
-      Dump_Freeze_Null    := Debug_Flag_S or Debug_Flag_G;
+      Dump_Freeze_Null    := Debug_Flag_S or Dump_Generated_Only;
 
       --  Note that we turn off the tree dump flags immediately, before
       --  starting the dump. This avoids generating two copies of the dump

gcc/ada/sprint.ads

@@ -97,7 +97,7 @@ package Sprint is
    --    -dg  print source from tree, including only the generated code
    --    -do  print source from tree, including only the original code
    --    -df  modify the above to include all units, not just the main unit
-   --    -sz  print source from tree for package Standard
+   --    -dz  print source from tree for package Standard
 
    procedure Sprint_Comma_List (List : List_Id);
    --  Prints the nodes in a list, with separating commas. If the list is empty

gcc/ada/switch-c.adb

@@ -451,7 +451,6 @@ package body Switch.C is
 
                Debug_Generated_Code := True;
                Xref_Active := False;
-               Set_Debug_Flag ('g');
 
             --  -gnate? (extended switches)