Remove unnecessary feature flags for optional deps

Author: h7kanna

ast/Cargo.toml

@@ -16,8 +16,6 @@ fold = []
 unparse = ["rustpython-literal"]
 visitor = []
 all-nodes-with-ranges = []
-malachite-bigint = ["dep:malachite-bigint"]
-num-bigint = ["dep:num-bigint"]
 
 [dependencies]
 rustpython-parser-core = { workspace = true }