WebGLProgram: Do not define USE_UV

[mrdoob]

Related issue: #25721

Description

This should hopefully fix this issue in drei:
https://twitter.com/0xca0a/status/1641555401073098752

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

Filesize	Gzipped	Diff from dev
627.3 kB	156 kB	-92 B

🌳 Bundle size after tree-shaking

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

Filesize	Gzipped	Diff from dev
418.9 kB	102.1 kB	-92 B

[Mugen87]

How is USE_UV now supposed to be set? The uv_* shader chunks still check the define.

[mrdoob]

I left the USE_UV code there because I noticed this pattern...

three.js/examples/jsm/shaders/SubsurfaceScatteringShader.js

Lines 41 to 44 in 4e361e9

	vertexShader: [
	'#define USE_UV',
	ShaderChunk[ 'meshphong_vert' ],
	].join( '\n' ),

three.js/examples/jsm/misc/ProgressiveLightMap.js

Lines 277 to 280 in 4e361e9

	shader.vertexShader =
	'#define USE_UV\n' +
	shader.vertexShader.slice( 0, - 1 ) +
	' gl_Position = vec4((uv - 0.5) * 2.0, 1.0, 1.0); }';

So I thought leaving a a couple of lines was worth it to not break an unknown amount of hacks... 😅