.readthedocs.yaml: remove system-packages

Upstream stopped supporting this.

Change-Id: I5839728f14b1a5822489f6cb64dbdd7c6f73ee03
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
diff --git a/.readthedocs.yaml b/.readthedocs.yaml
index e01c245..162e9fd 100644
--- a/.readthedocs.yaml
+++ b/.readthedocs.yaml
@@ -1,45 +1,26 @@
 # .readthedocs.yaml
-
 # Read the Docs configuration file
-
 # See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
-
 # Required
-
 version: 2
 
 # Set the version of Python and other tools you might need
-
 build:
-
   os: ubuntu-22.04
-
   tools:
-
     python: "3.10"
-
   apt_packages:
-
     - plantuml
 
 # Other variants to build than HTML
-
 formats: all
 
 # Build documentation in the docs/ directory with Sphinx
-
 sphinx:
-
    configuration: docs/conf.py
-
    fail_on_warning: true
 
 # Declare the Python requirements required to build your docs
-
 python:
-
    install:
-
    - requirements: docs/requirements.txt
-
-   system_packages: false