Remove expect tests for ecmaref compilation output (Closes #241)

The compiled interpreter generate a massive cesl program. Because of
this, when we change anything in the ecmaref interpreters the expect
tests of the ecmaref compilation command generate massive diffs.

To address this, we simply run `ecma-sl compile` and disregard the
compilation artifact into `dev/null`. This way, we rely on the parser
and typechecker to verify the validity of the esl program. If any of
these fail, the error messages (reported on stderr) will appear in the
expect test. Reducing diffs of PR that modify the ecmaref interpreters
while ensuring that the CI catches any errors.

JS-Interpreters/ecmaref5/empty.esl

@@ -0,0 +1,5 @@
+import "./esl_interpreter.esl";
+
+function main() {
+  return 0;
+}

JS-Interpreters/ecmaref6/empty.esl

@@ -0,0 +1,7 @@
+import "./esl_interpreter.esl";
+import "./bindings/ffi_symbolic.esl";
+import "./bindings/node-bindings.esl";
+
+function main() {
+  return 0;
+}

test/ecmaref/test_compile.t

@@ -0,0 +1,8 @@
+Change dir into `JS-Interpreters`
+  $ cd ../../JS-Interpreters
+
+Tests compilation of ecmaref5:
+  $ ecma-sl compile ecmaref5/empty.esl > /dev/null
+
+Tests compilation of ecmaref6:
+  $ ecma-sl compile ecmaref6/empty.esl > /dev/null