Remove parens from license expression.

license-exprs doesn't yet support parens:

ehuss/license-exprs#3

so remove them for now. The parens were redundant by the license expression
precedence rules in

https://spdx.org/spdx-specification-21-web-version.

Cargo.toml

@@ -2,7 +2,7 @@
 name = "wasi"
 version = "0.5.0"
 authors = ["The Cranelift Project Developers"]
-license = "(Apache-2.0 WITH LLVM-exception) OR Apache-2.0 OR MIT"
+license = "Apache-2.0 WITH LLVM-exception OR Apache-2.0 OR MIT"
 description = "Experimental WASI API bindings for Rust"
 edition = "2018"
 categories = ["no-std", "wasm"]