API: Removed constants DD_DMU_VERSION and DMUAPI_VER

Versioning of APIs is now handled with a special purpose mechanism,
so these old crutches are no longer necessary.

doomsday/api/dd_share.h

@@ -217,7 +217,6 @@ enum {
     DD_PLUGIN_NICENAME, ///< (e.g., jDoom, MyGame:Episode2 etc..., fancy name)
     DD_PLUGIN_HOMEURL,
     DD_PLUGIN_DOCSURL,
-    DD_DMU_VERSION, ///< Used in the exchange of DMU API versions.
     DD_DEF_ACTION,
 
     // Non-integer/special values for Set/Get
@@ -309,9 +308,6 @@ enum {
  */
 ///@{
 
-/// Public DMU API version number. Requested by the engine during init. @ingroup dmu
-#define DMUAPI_VER          1
-
 /// Map Update constants. @ingroup dmu
 enum {
     // Do not change the numerical values of the constants!

doomsday/plugins/common/src/common.c

@@ -27,9 +27,6 @@ int Common_GetInteger(int id)
 {
     switch(id)
     {
-    case DD_DMU_VERSION:
-        return DMUAPI_VER;
-
     case DD_GAME_RECOMMENDS_SAVING:
         // The engine will use this as a hint whether to remind the user to
         // manually save the game before, e.g., upgrading to a new version.