Fix build errors by removing references to non-existent apriltag-field-layout file

Removed references to apriltag-field-layout.rst which doesn't exist in this PR:
- Removed from toctree in index.rst
- Removed from "See Also" section in apriltag-pose-estimation.rst

The apriltag-field-layout article is being created in PR wpilibsuite#3138. Once that
PR merges, the references can be added back.

This fixes the build errors:
- "toctree contains reference to nonexisting document"
- "unknown document: 'apriltag-field-layout'"

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: jasondaming

source/docs/software/vision-processing/apriltag/apriltag-pose-estimation.rst

@@ -297,7 +297,6 @@ This approach requires solid understanding of 3D geometry and coordinate transfo
 
 ## See Also
 
-- :doc:`apriltag-field-layout` - Understanding and using AprilTag field layouts
 - :doc:`/docs/software/advanced-controls/state-space/state-space-pose-estimators` - Using pose estimators with vision measurements
 - :doc:`/docs/software/basic-programming/coordinate-system` - Understanding the FRC coordinate system
 - `PhotonVision Documentation <https://docs.photonvision.org/>`__ - Complete PhotonVision documentation

source/docs/software/vision-processing/apriltag/index.rst

@@ -4,5 +4,4 @@
    :maxdepth: 2
 
    apriltag-intro
-   apriltag-field-layout
    apriltag-pose-estimation