Revert "blank_screen: always exit with _exit()."

This was a temporary workaround in Android P, but it is fixed
with a relatively more dangerous change in libhwbinder.

This reverts commit 73ba34f1b7.

Bug: 77934844
Test: reboot device and watch for screen to get shutdown, check logs

Change-Id: I970144eea4acd8254f4a67ebe803f3c3eda9aba2

light/utils/main.cpp

@@ -55,6 +55,5 @@ int main() {
         }
     });
 
-    // b/77934844: Avoid running static destructors.
-    _exit(1);
+    return 0;
 }