Remove assertion that is no longer true and that does not do anything useful.

This assertion should have been removed with an earlier diff that made it no longer true.

hphp/runtime/vm/bytecode.cpp

@@ -1496,8 +1496,6 @@ Array VMExecutionContext::getCallerInfo() {
       Unit* unit = ar->m_func->unit();
       int lineNumber;
       if ((lineNumber = unit->getLineNumber(pc)) != -1) {
-        assert(!unit->filepath()->size() ||
-               unit->filepath()->data()[0] == '/');
         result.set(s_file, unit->filepath()->data(), true);
         result.set(s_line, lineNumber);
         return result;