[REG 2.064] Fix issue 11283 - Remove sysErrorString unittest

http://d.puremagic.com/issues/show_bug.cgi?id=11283

As noted in the bug report, it may be Windows 8 specific, but it's hard to tell what exactly causes it, or why US English error messages can be missing from Windows systems. In light of this, I can't think of a meaningful test that works on all Windows systems, so this PR removes the unittest entirely. The old `sysErrorString` did not have a unittest either, so it's not a net loss. At least the current incarnation of `sysErrorString` has been manually tested on systems of various language configurations.