build: remove simd-accel feature

This feature is no longer used, instead we rely on runtime CPU feature
detection. We kept the feature around as a no-op for backwards
compatibility, but no longer need to support it for regex 1.0.

Author: BurntSushi

Diff for: Cargo.toml

@@ -54,9 +54,6 @@ unstable = ["pattern"]
 # Enable to use the unstable pattern traits defined in std. This is enabled
 # by default if the unstable feature is enabled.
 pattern = []
-# Enable to use simd acceleration.
-# Note that this is deprecated and is a no-op.
-simd-accel = []
 
 [lib]
 # There are no benchmarks in the library code itself