Delete unused multibyte methods from PAL

[am11]

CreateProcessA had an occurrence in ToolBox, where LPSTR was converted to LPWSTR.

[am11]

cc @jkotas, this PR has not removed the A methods which are used by their W counterparts (e.g. SetEnvironmentVariableA, CopyFileA, MoveFileA etc.).

[davidwrighton]

@am11 Could you hold off on checking in any more changes that reformat code in the PAL tests for a week or so? My larger work item to return these tests to running in CI is running into repeated merge conflicts.

Thank you.

[am11]

Sure, sorry about the conflicts. I just realize it (few hours ago, #42049 (comment)). :(
I have a unix script which I run before checkin that removes trailing whitespaces from the code files, which are included in the commits from tip of my local branch to upstream's master:

#!/usr/bin/env sh

# assuming remote name 'dotnet' is present (after user/org GH naming)
# git remote dotnet https://github.com/dotnet/runtime

# if file exists in (combined) delta, clear the trailing white-spaces:
$ git show --name-only --pretty="" HEAD...dotnet/master |\
    xargs -I{} sh -c "test -f {} && sed -i '' 's/[[:space:]]*$//' {}"