chore: clean up temp test directories

_test_foundation/bux.toml

@@ -1,4 +0,0 @@
-[Package]
-Name = "test"
-Version = "0.1.0"
-Type = "bin"

_test_foundation/src/Main.bux

@@ -1,2 +0,0 @@
-import Std::Io::PrintLine;
-func Main() -> int { PrintLine("foundation ok"); return 0; }