[mlir][async] Update comments about library registration. (NFC)

This updates the code comments about the library registration mechanism,
which changed in https://reviews.llvm.org/D153029, and which should have
updated as part of that patch.

Reviewed By: ingomueller-net

Differential Revision: https://reviews.llvm.org/D153147

Author: ingomueller-net

mlir/lib/ExecutionEngine/AsyncRuntime.cpp

@@ -452,10 +452,11 @@ extern "C" void mlirAsyncRuntimePrintCurrentThreadId() {
 }
 
 //===----------------------------------------------------------------------===//
-// MLIR Runner (JitRunner) dynamic library integration.
+// MLIR ExecutionEngine dynamic library integration.
 //===----------------------------------------------------------------------===//
 
-// Export symbols for the MLIR runner integration. All other symbols are hidden.
+// Export symbols for the MLIR ExecutionEngine integration. All other symbols
+// are hidden.
 #ifdef _WIN32
 #define API __declspec(dllexport)
 #else