Remove unnecessary required feature metadata for tonemapping example (#8970)

# Objective

These features are now included by default, so this metadata is no
longer required.

See #8657 (comment)

## Solution

Remove the metadata

Author: rparrett

Cargo.toml

@@ -570,7 +570,6 @@ wasm = true
 [[example]]
 name = "tonemapping"
 path = "examples/3d/tonemapping.rs"
-required-features = ["ktx2", "zstd"]
 
 [package.metadata.example.tonemapping]
 name = "Tonemapping"