[Ada] Refactor duplicate code for pretty-printing GNAT AST

[Pierre-Marie de Rodat via Gcc-patches]

Remove duplicated CASE branches detected by infer; semantics is
unaffected.

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

gcc/ada/

        * sprint.adb (Sprint_Node_Actual): Refactor code for generic
        package and subprogram declarations.
diff --git a/gcc/ada/sprint.adb b/gcc/ada/sprint.adb
--- a/gcc/ada/sprint.adb
+++ b/gcc/ada/sprint.adb
@@ -2075,7 +2075,7 @@ package body Sprint is
             Sprint_Node (Name (Node));
             Write_Char (';');
 
-         when N_Generic_Package_Declaration =>
+         when N_Generic_Declaration =>
             Extra_Blank_Line;
             Write_Indent_Str_Sloc ("generic ");
             Sprint_Indented_List (Generic_Formal_Declarations (Node));
@@ -2097,14 +2097,6 @@ package body Sprint is
             Sprint_Node (Name (Node));
             Write_Char (';');
 
-         when N_Generic_Subprogram_Declaration =>
-            Extra_Blank_Line;
-            Write_Indent_Str_Sloc ("generic ");
-            Sprint_Indented_List (Generic_Formal_Declarations (Node));
-            Write_Indent;
-            Sprint_Node (Specification (Node));
-            Write_Char (';');
-
          when N_Goto_Statement =>
             Write_Indent_Str_Sloc ("goto ");
             Sprint_Node (Name (Node));