scripts/test: Clean old unit tests before building new ones to avoid confusion

if a unit test fails to build and old unit tests remain in place, this can
lead to confusion when the old test is run anyway.

"Why are some test cases missing?"
"Huh, it failed to build but passed?"

scripts/test.sh

@@ -25,6 +25,8 @@ else
 fi
 echo "$LD_LIBRARY_PATH"
 
+echo ">>> Cleaning tests..."
+remove bin/test
 create_directory bin/test
 
 echo ">>> Building tests..."