Crate does not build due to stdarch_arm_crc32 feature

[Philip Deuchler]

stdarch_arm_crc32 is now stable and use of the feature flag will fail builds:

error[E0635]: unknown feature `stdarch_arm_crc32`
  --> /usr/local/cargo/registry/src/index.crates.io-6f17d22bba15001f/pathfinder_simd-0.5.3/src/lib.rs:13:69
   |
13 | #![cfg_attr(all(target_arch = "aarch64", pf_rustc_nightly), feature(stdarch_arm_crc32))]