Rely on docs.rs to define --cfg=docsrs by default

Cargo.toml

@@ -34,7 +34,7 @@ doc-scrape-examples = false
 [package.metadata.docs.rs]
 features = ["preserve_order", "raw_value", "unbounded_depth"]
 targets = ["x86_64-unknown-linux-gnu"]
-rustdoc-args = ["--cfg", "docsrs", "--generate-link-to-definition"]
+rustdoc-args = ["--generate-link-to-definition"]
 
 [package.metadata.playground]
 features = ["raw_value"]