Fix environment compilation error:

```
bazel build //litert/c:litert_environment  --//litert/build_common:build_include=gpu
...
litert/c/litert_environment.cc:46:11: error: no type named 'TriggerAcceleratorAutomaticRegistration' in namespace 'litert'
   46 |   litert::TriggerAcceleratorAutomaticRegistration(*env);
```

LiteRT-PiperOrigin-RevId: 826266539

Author: MatthiasKreileder

litert/c/BUILD

@@ -145,13 +145,9 @@ cc_library(
         ":litert_environment_options",
         "//litert/cc:litert_macros",
         "//litert/core:environment",
+        "//litert/runtime/accelerators:auto_registration",
         "@com_google_absl//absl/types:span",
     ] + select({
-        "//litert/build_common:build_include_npu_enabled": [
-            "//litert/runtime/accelerators:auto_registration",
-        ],
-        "//conditions:default": [],
-    }) + select({
         "//litert/build_common:build_include_gpu_enabled": [
             "//litert/runtime:gpu_environment",
         ],

litert/c/litert_environment.cc

@@ -23,9 +23,7 @@
 #include "litert/c/litert_environment_options.h"
 #include "litert/cc/litert_macros.h"
 #include "litert/core/environment.h"
-#if !defined(LITERT_DISABLE_NPU)
 #include "litert/runtime/accelerators/auto_registration.h"
-#endif  // !defined(LITERT_DISABLE_NPU)
 #if !defined(LITERT_DISABLE_GPU)
 #include "litert/runtime/gpu_environment.h"
 #endif  // !defined(LITERT_DISABLE_GPU)