Remove build dependencies

They were used before the separate proc-macro crate was created, but
aren't anymore.

Author: glandium

Cargo.toml

@@ -27,11 +27,6 @@ phf = {version = ">=0.8,<=0.11", features = ["macros"]}
 serde = {version = "1.0", optional = true}
 smallvec = "1.0"
 
-[build-dependencies]
-syn = { version = "1", features = ["extra-traits", "fold", "full"] }
-quote = "1"
-proc-macro2 = "1"
-
 [features]
 bench = []
 dummy_match_byte = []