Fix build: remove invalid JniException constructor call

JniException takes a jthrowable, not a string. throwExecutorchException
already throws via fbjni at the JNI boundary — no need to rethrow.

This commit was authored with the help of Claude.

Author: psiddh

extension/android/jni/jni_layer.cpp

@@ -288,17 +288,13 @@ class ExecuTorchJni : public facebook::jni::HybridClass<ExecuTorchJni> {
       module_ = std::make_unique<Module>(
           modelPath->toStdString(), load_mode, std::move(etdump_gen));
     } catch (const std::exception& e) {
-      const std::string error_message =
-          std::string("Failed to create Module: ") + e.what();
       executorch::jni_helper::throwExecutorchException(
-          static_cast<uint32_t>(Error::Internal), error_message);
-      throw facebook::jni::JniException(error_message);
+          static_cast<uint32_t>(Error::Internal),
+          std::string("Failed to create Module: ") + e.what());
     } catch (...) {
-      constexpr const char* error_message =
-          "Failed to create Module: unknown native error";
       executorch::jni_helper::throwExecutorchException(
-          static_cast<uint32_t>(Error::Internal), error_message);
-      throw facebook::jni::JniException(error_message);
+          static_cast<uint32_t>(Error::Internal),
+          "Failed to create Module: unknown native error");
     }
 
 #ifdef ET_USE_THREADPOOL