Remove unneeded lib name from Cargo.toml

This is left over from the proc-macro2-next preview releases.

Author: dtolnay

Cargo.toml

@@ -15,9 +15,6 @@ option, off by default, to also reimplement itself in terms of the upstream
 unstable API.
 """
 
-[lib]
-name = "proc_macro2"
-
 [package.metadata.docs.rs]
 rustc-args = ["--cfg", "procmacro2_semver_exempt"]
 rustdoc-args = ["--cfg", "procmacro2_semver_exempt"]