Remove non-existent feature from README

The feature was removed in PR apache#674, but the feature list in the README wasn't updated

arrow/README.md

@@ -46,7 +46,6 @@ The `arrow` crate provides the following features which may be enabled in your `
 - `ipc` (default) - support for reading [Arrow IPC Format](https://arrow.apache.org/docs/format/Columnar.html#serialization-and-interprocess-communication-ipc), also used as the wire protocol in [arrow-flight](https://crates.io/crates/arrow-flight)
 - `ipc_compression` - Enables reading and writing compressed IPC streams (also enables `ipc`)
 - `prettyprint` - support for formatting record batches as textual columns
-- `js` - support for building arrow for WebAssembly / JavaScript
 - `simd` - (_Requires Nightly Rust_) Use alternate hand optimized
   implementations of some [compute](https://github.com/apache/arrow-rs/tree/master/arrow/src/compute/kernels)
   kernels using explicit SIMD instructions via [packed_simd_2](https://docs.rs/packed_simd_2/latest/packed_simd_2/).