WebGPUBackend: Remove obsolete argument from getDrawingBufferSize().

[Mugen87]

Related issue: #31450 (comment)

Description

The PR removes obsolete arguments from Backend.getDrawingBufferSize() calls.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	338.04 78.86	338.04 78.86	+0 B +0 B
WebGPU	559.11 154.78	559.09 154.77	-19 B -7 B
WebGPU Nodes	558.03 154.56	558.01 154.55	-19 B -10 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

	Before	After	Diff
WebGL	469.29 113.56	469.29 113.56	+0 B +0 B
WebGPU	634.4 171.81	634.38 171.81	-20 B -6 B
WebGPU Nodes	589.53 161.13	589.51 161.12	-20 B -17 B