Very old shells suffered from bugs which meant that prefixing variables
with an "x" to ensure that the lefthand side of a comparison always
started with an alphanumeric character was needed. Modern shells don't
suffer from this issue (i.e Bash was fixed in 1996).
In any case, we've already got unprefixed checks used in our codebase,
i.e https://github.com/bitcoin/bitcoin/blob/master/configure.ac#L292,
and have dependencies (in depends) that also use unprefixed comparisons.
I think it's time that we can consolidate on not using the x-prefix
workaround. At best it's mostly just confusing.
More info:
https://github.com/koalaman/shellcheck/wiki/SC2268https://www.vidarholen.net/contents/blog/?p=1035
