Revert^2 "lshal: use std::async"

This reverts commit 2cfbc514764472becab46b41ebe0323a68369cad.

Reason for revert: reapply change

Bug: 323268003
Bug: 311143089
Test: See next CL
Change-Id: I392eca8f3368c1d74b4de37d5f49663d3ddbf7e0
diff --git a/cmds/lshal/main.cpp b/cmds/lshal/main.cpp
index 366c938..bd5fa32 100644
--- a/cmds/lshal/main.cpp
+++ b/cmds/lshal/main.cpp
@@ -18,5 +18,6 @@
 
 int main(int argc, char **argv) {
     using namespace ::android::lshal;
-    return Lshal{}.main(Arg{argc, argv});
+    // Use _exit() to force terminate background threads in Timeout.h
+    _exit(Lshal{}.main(Arg{argc, argv}));
 }