Fix refs to hardware-context-reset and internal-error (#548)

The prose incorrectly referenced `{{MediaKeyStatus/"hardware-context-reset"}}`
which does not exist, instead of using the `MediaKeySessionClosedReason` enum.

The CDM Unavailable algorithm takes a `MediaKeySessionClosedReason` value as
input, so the references to `{{MediaKeyStatus/"internal-error"}}` were
incorrect too.

Author: tidoust

encrypted-media-respec.html

@@ -6249,8 +6249,9 @@ 
                     <li>
                       <p>
                         Run the [=CDM Unavailable=] algorithm on <var>media keysvar> with the
-                        reason {{MediaKeyStatus/"hardware-context-reset"}} for a hardware context
-                        reset or {{MediaKeyStatus/"internal-error"}} otherwise.
+                        reason {{MediaKeySessionClosedReason/"hardware-context-reset"}} for a
+                        hardware context reset or {{MediaKeySessionClosedReason/"internal-error"}}
+                        otherwise.
                       p>
                     li>
                     <li>
@@ -6354,9 +6355,10 @@ 
                                       <p>
                                         If <var>cdmvar> is no longer usable, run the [=CDM
                                         Unavailable=] algorithm on <var>media keysvar> with the
-                                        reason {{MediaKeyStatus/"hardware-context-reset"}} for a
-                                        hardware context reset, or
-                                        {{MediaKeyStatus/"internal-error"}} otherwise.
+                                        reason
+                                        {{MediaKeySessionClosedReason/"hardware-context-reset"}}
+                                        for a hardware context reset, or
+                                        {{MediaKeySessionClosedReason/"internal-error"}} otherwise.
                                       p>
                                     li>
                                     <li>