Revert "fix: check key type in externals dict (#270)"

This reverts commit 3c616fe.

Author: plusvic

yara-python.c

@@ -1522,13 +1522,6 @@ int process_compile_externals(
 
   while (PyDict_Next(externals, &pos, &key, &value))
   {
-    if (!PY_STRING_CHECK(key)) {
-      PyErr_Format(
-          PyExc_TypeError,
-          "keys of externals dict must be strings");
-
-      return ERROR_INVALID_ARGUMENT;
-    }
     identifier = PY_STRING_TO_C(key);
 
     if (PyBool_Check(value))
@@ -1599,13 +1592,6 @@ int process_match_externals(
 
   while (PyDict_Next(externals, &pos, &key, &value))
   {
-    if (!PY_STRING_CHECK(key)) {
-      PyErr_Format(
-          PyExc_TypeError,
-          "keys of externals dict must be strings");
-
-      return ERROR_INVALID_ARGUMENT;
-    }
     identifier = PY_STRING_TO_C(key);
 
     if (PyBool_Check(value))