Revert "lshal: use std::async"

This reverts commit 9e509aba9efba4de1253acd332745521d571a474.

Reason for revert: broke adb shell lshal debug
Bug: 323268003

Change-Id: I005ae901dc347a0f4d3ad617ab148c8023786e7b
diff --git a/cmds/lshal/main.cpp b/cmds/lshal/main.cpp
index bd5fa32..366c938 100644
--- a/cmds/lshal/main.cpp
+++ b/cmds/lshal/main.cpp
@@ -18,6 +18,5 @@
 
 int main(int argc, char **argv) {
     using namespace ::android::lshal;
-    // Use _exit() to force terminate background threads in Timeout.h
-    _exit(Lshal{}.main(Arg{argc, argv}));
+    return Lshal{}.main(Arg{argc, argv});
 }