examples/sotest: fix issue about running multiple times

Signed-off-by: dongjiuzhu1 <dongjiuzhu1@xiaomi.com>

examples/sotest/sotest_main.c

@@ -36,6 +36,7 @@
 #include <dlfcn.h>
 #include <errno.h>
 #include <debug.h>
+#include <unistd.h>
 
 #include <nuttx/symtab.h>
 
@@ -282,6 +283,8 @@ int main(int argc, FAR char *argv[])
               BINDIR, errno);
       exit(EXIT_FAILURE);
     }
+
+  unlink(devname);
 #endif /* CONFIG_EXAMPLES_SOTEST_BUILTINFS */
 
   return EXIT_SUCCESS;