Simplify cargo features exposed by the crate #911

Job	Run time
test_avif	1m 6s
clippy	2m 55s
test_avif_decoding	2m 11s
Fuzz targets (afl)	1m 50s
test_big_endian	1m 17s
test_big_endian (default)	4m 32s
test_big_endian (webp-native)	1m 39s
test_toolchains (1.64.0)	2m 11s
test_toolchains (nightly)	3m 54s
test_toolchains (beta)	3m 59s
test_features	1m 13s
test_features (default)	3m 15s
test_features (gif)	1m 4s
test_features (jpeg)	1m 21s
test_features (png)	1m 20s
test_features (tiff)	1m 15s
test_features (ico)	1m 29s
test_features (pnm)	1m 3s
test_features (tga)	1m 17s
test_features (webp)	1m 29s
test_features (bmp)	1m 22s
test_features (hdr)	1m 1s
test_features (dxt)	59s
test_features (dds)	1m 1s
test_features (ff)	57s
test_features (exr)	1m 34s
test_features (parallel)	1m 18s
test_features (webp-native)	1m 13s
test_features (avif-native)	1m 0s
build_benchmarks	1m 57s
Fuzz targets (cargo-fuzz)	3m 40s
cargo-deny	30s
public_private_dependencies	45s
rustfmt	17s
verify_msrv	2m 9s
	1h 0m 3s

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