Delete the implementation of DML backend and disable CI

Author: mingmingtasd

.github/workflows/build_test_dml.yml

@@ -210,19 +210,6 @@ source_set("sources") {
     }
   }
 
-  if (webnn_enable_dml) {
-   sources += [
-      "dml/BackendDML.cpp",
-      "dml/BackendDML.h",
-      "dml/ContextDML.cpp",
-      "dml/ContextDML.h",
-      "dml/GraphDML.cpp",
-      "dml/GraphDML.h",
-      "dml/DMLUtils.cpp",
-      "dml/DMLUtils.h",
-    ]
-  }
-
   if (webnn_enable_dmlx) {
     if (webnn_enable_gpu_buffer == false) {
       sources += [