message: Remove ENV variable enabling grappler pass
  Keeping the wrapper function for use when loss scaling interaction
  is finalized
diff: @@ -124,16 +124,7 @@ bool AutoMixedPrecisionEnabled(RewriterConfig::Toggle opt_level) {
  opt_level == RewriterConfig::AGGRESSIVE) {
  return true;
  }
  - if (opt_level == RewriterConfig::OFF) return false;
  - // Default is to check env var, otherwise off.
  - static bool is_enabled = [] {
  - bool ret = false;
  - TF_CHECK_OK(
  - ReadBoolFromEnvVar("TF_ENABLE_AUTO_MIXED_PRECISION_GRAPH_REWRITE",
  - /*default_val=*/false, &ret));
  - return ret;
  - }();
  - return is_enabled;
  + return false;
  }
  } // namespace
  