stdout/stderr around
A lot of functions in the cmd and ctl packages were passing these
around and barely using them. Replaced them with a logger for most
functions. Some functions get an io.Writer instead so that their
tests can find the output they're looking for.
More cleanup on fb-1766: reworked the tests that were using io.Pipe
or os.Pipe to check their results so they now use a bytes.Buffer.
Unexported some variables that didn't need to be exported.
Fixed NewConfigCommand to use the provided stderr, not os.Stderr.
Added tests for rbf_dump, rbf_page, and keygen, since those weren't
being tested at all.
Added chksum_test, final cleanup.
(cherry picked from commit f627199acb)
* removes unused filesize function
* removes ioutil usage
* updates ioutil.ReadAll to io.ReadAll
* updates ioutil.TempFile to os.CreateTemp
* updates ioutil.TempDir to os.MkdirTemp
* updates ioutil.ReadAll to os.ReadAll
* update ioutil.WriteFile to os.WriteFile
* updates ioutil.Discard to io.Discard
* updates ioutil.ReadDir to os.ReadDir where applicable
* removes unused code in idk
* creates type to use for context value keys
* replaces assert.Nil with assert.NoError for error checks