Bug 1721515 - qcms: Remove some now unneeded unstable features. r=aosmond

These were used by our local NEON intrinsics implementation.
We don't need them anymore.

Differential Revision: https://phabricator.services.mozilla.com/D120420

gfx/qcms/src/lib.rs

@@ -5,10 +5,9 @@
 #![allow(non_camel_case_types)]
 #![allow(non_snake_case)]
 #![allow(non_upper_case_globals)]
+// These are needed for the neon SIMD code and can be removed once the MSRV supports the
+// instrinsics we use
 #![cfg_attr(feature = "neon", feature(stdsimd))]
-// These are needed for the neon intrinsics implementation
-// and can be removed once the MSRV is high enough (1.48)
-#![cfg_attr(feature = "neon", feature(platform_intrinsics, simd_ffi, link_llvm_intrinsics))]
 #![cfg_attr(feature = "neon", feature(aarch64_target_feature, arm_target_feature, raw_ref_op))]
 
 /// These values match the Rendering Intent values from the ICC spec