Unbreak build with Rust 1.45.0

error: options `-C embed-bitcode=no` and `-C lto` are incompatible

--- config/makefiles/rust.mk.orig	2020-05-12 09:36:22 UTC
+++ config/makefiles/rust.mk
@@ -61,7 +61,7 @@ ifndef MOZ_DEBUG_RUST
 # Enable link-time optimization for release builds, but not when linking
 # gkrust_gtest.
 ifeq (,$(findstring gkrust_gtest,$(RUST_LIBRARY_FILE)))
-cargo_rustc_flags += -Clto
+cargo_rustc_flags += 
 endif
 endif
 endif