Use license instead of license-file (#1189)

Per the Cargo Book, `license-file` is only to be used if a package uses
a non-standard license; see https://doc.rust-lang.org/cargo/reference/manifest.html#the-license-and-license-file-fields

Declare the licenses directly, and verify that the LICENSE file
containing the license breakdown is still included

```
…n LibCST/native/libcst_derive on  cargo-fixes [!] is 📦 v1.4.0 via 🦀 v1.77.1
⬢ [fedora:40] ❯ cargo package --list --allow-dirty | grep LICENSE
LICENSE

…n LibCST/native/libcst_derive on  cargo-fixes [!] is 📦 v1.4.0 via 🦀 v1.77.1
⬢ [fedora:40] ❯ cd ../libcst

michel in LibCST/native/libcst on  cargo-fixes [!] is 📦 v1.4.0 via 🦀 v1.77.1
⬢ [fedora:40] ❯ cargo package --list --allow-dirty | grep LICENSE
LICENSE
src/tokenizer/core/LICENSE
```

Signed-off-by: Michel Lind <salimma@fedoraproject.org>

native/libcst/Cargo.toml

@@ -10,7 +10,7 @@ authors = ["LibCST Developers"]
 edition = "2018"
 rust-version = "1.70"
 description = "A Python parser and Concrete Syntax Tree library."
-license-file = "LICENSE"
+license = "MIT AND (MIT AND PSF-2.0)"
 repository = "https://github.com/Instagram/LibCST"
 documentation = "https://libcst.rtfd.org"
 keywords = ["python", "cst", "ast"]

native/libcst_derive/Cargo.toml

@@ -3,7 +3,7 @@ name = "libcst_derive"
 version = "1.4.0"
 edition = "2018"
 description = "Proc macro helpers for libcst."
-license-file = "LICENSE"
+license = "MIT"
 repository = "https://github.com/Instagram/LibCST"
 documentation = "https://libcst.rtfd.org"
 keywords = ["macros", "python"]