Revert "Change all instances of 'whitelist' to 'allowlist'"

[xtqqczze]

This reverts commit cd09bb671aa892e13ca5ad71dfb7c4d49ab38c80.

cc: @alerickson, @TravisEz13, @adityapatwardhan

It is confusing to change instances of whitelist in comments and changelog, given that the term is referring to the following PowerShell variable:

https://github.com/PowerShell/PowerShellGetv2/blob/7ef9df4738fbe2eefb144ff94b8941da0ccdec7f/src/PowerShellGet/private/modulefile/PartOne.ps1#L320-L323

[xtqqczze]

Google recommends against using the terms: allowlist (verb), allowlisted, allowlisting, see:

https://developers.google.com/style/word-list#allowlist