Fixed three LC_ALL settings:

1) Replaced en_US.ISO8859-1 with C because that's sufficient to show
   decoding with an invalid multibyte sequence.
2) Removed redundant LC_ALL=en_US.UTF-8; that is set for the entire test.
3) Removed the last en_US.ISO8859-1 because it hid what the test was
   trying to show.