Relicense dispatch2 under Zlib as well

Permission given in:
marysaka/dispatch2#2 (comment)

LICENSE.md

@@ -3,8 +3,6 @@
 The licensing of these crates is a bit complicated:
 - The crates `objc2`, `block2`, `objc2-foundation` and `objc2-encode` are
   [currently][#23] licensed under [the MIT license][MIT].
-- The `dispatch2` crate is dual-licensed under the [Apache-2.0] or [MIT]
-  license, at your option.
 - All other crates are trio-licensed under the [Zlib], [Apache-2.0] or [MIT]
   license, at your option.
 

crates/dispatch2/Cargo.modified.toml

@@ -3,7 +3,6 @@ version = "0.1.0" # Remember to update html_root_url in lib.rs
 description = "Bindings and wrappers for Apple's Grand Central Dispatch (GCD)"
 keywords = ["gcd", "macos", "ios", "dispatch", "libdispatch"]
 authors = ["Mads Marquart <[email protected]>", "Mary <[email protected]>"]
-license = "Apache-2.0 OR MIT"
 
 [dev-dependencies]
 static_assertions = "1.1.0"

crates/dispatch2/Cargo.toml

@@ -10,7 +10,7 @@ rust-version.workspace = true
 keywords = ["gcd", "macos", "ios", "dispatch", "libdispatch"]
 categories.workspace = true
 repository.workspace = true
-license = "Apache-2.0 OR MIT"
+license.workspace = true
 authors = ["Mads Marquart <[email protected]>", "Mary <[email protected]>"]
 
 [lints]