ada: Tech debt: Remove Aspect_Unimplemented

It's time to remove this temporary code;
the comment "-- ??? temp for now" was inserted in 2015.

gcc/ada/ChangeLog:

	* aspects.ads (Aspect_Unimplemented): Remove.
	* sem_ch13.adb (Aspect_Unimplemented): Remove.

gcc/ada/aspects.ads

diff --git a/gcc/ada/aspects.ads b/gcc/ada/aspects.ads
index 7b12775..d9d6fed 100644
--- a/gcc/ada/aspects.ads
+++ b/gcc/ada/aspects.ads
@@ -164,7 +164,6 @@
       Aspect_Taint_Source,                  -- GNAT
       Aspect_Test_Case,                     -- GNAT
       Aspect_Type_Invariant,
-      Aspect_Unimplemented,                 -- GNAT
       Aspect_Unsuppress,
       Aspect_User_Aspect,                   -- GNAT
       Aspect_Value_Size,                    -- GNAT
@@ -363,7 +362,6 @@
       Aspect_Suppress_Initialization    => True,
       Aspect_Test_Case                  => True,
       Aspect_Thread_Local_Storage       => True,
-      Aspect_Unimplemented              => True,
       Aspect_Universal_Aliasing         => True,
       Aspect_Unmodified                 => True,
       Aspect_Unreferenced               => True,
@@ -529,7 +527,6 @@
       Aspect_Synchronization            => Name,
       Aspect_Test_Case                  => Expression,
       Aspect_Type_Invariant             => Expression,
-      Aspect_Unimplemented              => Optional_Expression,
       Aspect_Unsuppress                 => Name,
       Aspect_User_Aspect                => Expression,
       Aspect_Value_Size                 => Expression,
@@ -637,7 +634,6 @@
       Aspect_Synchronization              => False,
       Aspect_Test_Case                    => False,
       Aspect_Type_Invariant               => False,
-      Aspect_Unimplemented                => False,
       Aspect_Unsigned_Base_Range          => True,
       Aspect_Unsuppress                   => False,
       Aspect_User_Aspect                  => False,
@@ -860,7 +856,6 @@
       Aspect_Test_Case                    => Name_Test_Case,
       Aspect_Type_Invariant               => Name_Type_Invariant,
       Aspect_Unchecked_Union              => Name_Unchecked_Union,
-      Aspect_Unimplemented                => Name_Unimplemented,
       Aspect_Universal_Aliasing           => Name_Universal_Aliasing,
       Aspect_Unmodified                   => Name_Unmodified,
       Aspect_Unreferenced                 => Name_Unreferenced,
@@ -1135,7 +1130,6 @@
       Aspect_Super                        => Never_Delay,
       Aspect_Synchronization              => Never_Delay,
       Aspect_Test_Case                    => Never_Delay,
-      Aspect_Unimplemented                => Never_Delay,
       Aspect_User_Aspect                  => Never_Delay,
       Aspect_Volatile_Function            => Never_Delay,
       Aspect_Warnings                     => Never_Delay,

gcc/ada/sem_ch13.adb

diff --git a/gcc/ada/sem_ch13.adb b/gcc/ada/sem_ch13.adb
index 9d48117..388f1ad 100644
--- a/gcc/ada/sem_ch13.adb
+++ b/gcc/ada/sem_ch13.adb
@@ -3768,10 +3768,7 @@
             --  Processing based on specific aspect
 
             case A_Id is
-               when Aspect_Unimplemented =>
-                  null; -- ??? temp for now
-
-               --  No_Aspect should be impossible
+               --  No_Aspect is impossible
 
                when No_Aspect =>
                   raise Program_Error;
@@ -12439,7 +12436,6 @@
             | Aspect_Super
             | Aspect_Suppress
             | Aspect_Test_Case
-            | Aspect_Unimplemented
             | Aspect_Unsuppress
             | Aspect_User_Aspect
             | Ignored_Aspects