Remove lib name from Cargo.toml

This is left over from the 0.15-rc versions which used [package] name =
"syn-next" and [lib] name = "syn".
diff --git a/Cargo.toml b/Cargo.toml
index 4ea1cc4..87f418e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -17,9 +17,6 @@
     "/src/**/*.rs",
 ]
 
-[lib]
-name = "syn"
-
 [features]
 default = ["derive", "parsing", "printing", "clone-impls", "proc-macro"]
 derive = []