Converting GLSL to Godot shaders/Macros: Outdated information about defines

[PoolloverNathan]

Your Godot version:
4.0

Issue description:
The Macros section on "Converting GLSL to Godot shaders" states that macros will need to be converted. However, Godot 4.0 allows using preprocessor macros inside shaders.

URL to the documentation page

PR: #7007