Remove readFile() and reverseSlice() in favour of stdlib (#671) #1103

Job	Run time
examples / client (ubuntu-latest)	14s
examples / multirepo (ubuntu-latest)	14s
examples / client (macos-latest)	14s
examples / client (windows-latest)	1m 23s
examples / multirepo (macos-latest)	13s
examples / multirepo (windows-latest)	1m 36s
examples / repository (ubuntu-latest)	14s
examples / repository (macos-latest)	14s
examples / root-signing (ubuntu-latest)	19s
examples / repository (windows-latest)	1m 20s
examples / root-signing (macos-latest)	19s
examples / root-signing (windows-latest)	1m 43s
examples / tuf-client-cli (ubuntu-latest)	19s
linting / govulncheck	29s
examples / tuf-client-cli (macos-latest)	19s
examples / tuf-client-cli (windows-latest)	1m 45s
linting / golangci-lint	2m 37s
tests / Run (ubuntu-latest)	37s
tests / Run (macos-latest)	29s
tests / Run (windows-latest)	2m 31s
	17m 9s

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