README: remove dead link to @wm4

RIP

README.md

@@ -183,12 +183,11 @@ best overall image quality, and so forth.
 
 libplacebo was founded and primarily developed by Niklas Haas
 ([@haasn](https://github.com/haasn)), but it would not be possible without the
-contributions of others. Special note also goes out
-([@wm4](https://github.com/wm4)), the developer of mpv, whose ideas helped
-shape the foundation of the shader dispatch system. This library also includes
-various excerpts from mpv, in particular the filter kernel code. For a full
-list of past contributors to mpv, see the [mpv authorship
-page](https://github.com/mpv-player/mpv/graphs/contributors)
+contributions of others. Special note also goes out to wm4, the developer of
+mpv, whose ideas helped shape the foundation of the shader dispatch system.
+This library also includes various excerpts from mpv, in particular the filter
+kernel code. For a full list of past contributors to mpv, see the [mpv
+authorship page](https://github.com/mpv-player/mpv/graphs/contributors)
 
 [![contributor list](https://opencollective.com/libplacebo/contributors.svg?width=890&button=false)](https://github.com/haasn/libplacebo/graphs/contributors)