Fix RTD build (#1694)

Author: sanketverma1704

.readthedocs.yaml

@@ -16,4 +16,6 @@ python:
       extra_requirements:
         - docs
 
-formats: all
+formats:
+  - htmlzip
+  - pdf

docs/index.rst

@@ -19,7 +19,7 @@ Zarr-Python
 
 **Version**: |version|
 
-**Download documentation**: `PDF/Zipped HTML/EPUB <https://readthedocs.org/projects/zarr/downloads/>`_
+**Download documentation**: `PDF/Zipped HTML <https://readthedocs.org/projects/zarr/downloads/>`_
 
 **Useful links**:
 `Installation <installation.html>`_ |