docs/environment: do not require yosys

Signed-off-by: Unai Martinez-Corral <umartinezcorral@antmicro.com>
diff --git a/docs/environment.yml b/docs/environment.yml
index 7100f6f..d8345d8 100644
--- a/docs/environment.yml
+++ b/docs/environment.yml
@@ -20,7 +20,6 @@
 dependencies:
 - python=3.8
 - pip
-- yosys
 - netlistsvg
 # Packages installed from PyPI
 - pip: