Remove explicit `feature(external_doc)`

It looks like this is now enabled by default as of `cargo 1.54.0-nightly (0cecbd673 2021-06-01)`

diff --git a/src/lib.rs b/src/lib.rs
index 77cbef619edb3fae680e014e899818780183028b..756e442953c0f058ebacc03d3f9d46a07ab2dd47 100644 (file)
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -14,9 +14,6 @@
 // only enables the `doc_cfg` feature when
 // the `docsrs` configuration attribute is defined
 #![cfg_attr(docsrs, feature(doc_cfg))]
-// only enables the nightly `external_doc` feature when
-// `test-md-docs` is enabled
-#![cfg_attr(feature = "test-md-docs", feature(external_doc))]
 
 //! A modern, lightweight, descriptor-based wallet library written in Rust.
 //!