alpkit: Remove base64 feature flag #42

Job	Run time
Run linters	28s
Test on x86_64-alpine-linux-musl (dynamically linked)	57s
Test with --features base64	16s
Test with --features shell-timeout	20s
Test with --features flate2-zlib --no-default-features	20s
Test with --features flate2-zlib-ng --no-default-features	19s
Test on x86_64-unknown-linux-musl with Rust stable	46s
Test on x86_64-unknown-linux-musl with Rust nightly	40s
Test on x86_64-unknown-linux-musl with Rust 1.64	57s
Test on x86_64-unknown-linux-gnu with Rust stable	47s
Test on x86_64-apple-darwin with Rust stable	54s
Test on aarch64-unknown-linux-musl with Rust stable	1m 30s
Test on aarch64-unknown-linux-gnu with Rust stable	57s
Test on armv7-unknown-linux-musleabihf with Rust stable	1m 16s
Test on powerpc64le-unknown-linux-gnu with Rust stable	1m 22s
Test on riscv64gc-unknown-linux-gnu with Rust stable	1m 17s
	13m 6s

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