docs: disable PDF output for documentation generation

Change-Id: I827deeb8008f0bf5f44c1f9d4afcce21ef102bba
diff --git a/.readthedocs.yaml b/.readthedocs.yaml
index 6e6fa84..2b418ae 100644
--- a/.readthedocs.yaml
+++ b/.readthedocs.yaml
@@ -22,8 +22,3 @@
 
 sphinx:
   configuration: docs/conf.py
-
-# Auxiliary formats to export to (in addition to the default HTML output).
-formats:
-  - pdf
-