Remove subproc events when ADB_HOST.

The code which triggers these events (via the SHELL_EXIT_NOTIFY_FD) are
only called from code which is already guarded by #if !ADB_HOST.

Change-Id: I184414f5e090c1f08ee117e4c8c434cd4a8b5221
diff --git a/adb/adb.h b/adb/adb.h
index 1be83d7..31fe3a5 100644
--- a/adb/adb.h
+++ b/adb/adb.h
@@ -365,7 +365,9 @@
 
 extern const char *adb_device_banner;
 extern int HOST;
+#if !ADB_HOST
 extern int SHELL_EXIT_NOTIFY_FD;
+#endif // !ADB_HOST
 
 #define CHUNK_SIZE (64*1024)