Revert "t4041: ensure the utf-8 encoded string really gets stored as utf-8."

This reverts commit 2482bc95bfb321bae3bb70d6516df53efc631261.
Revert "t7102: do not assume the system encoding is utf-8"

This reverts commit a0530b4ffca5c5f4a631c15e057b901f57312274.
t4041, t7102: do not pass iso8859-1 parameter

git commit -m with some iso8859-1 encoded stuff is doomed to fail in MinGW,
because Windows don't let you pass encoded bytes to a process (CreateProcessW
always takes a UTF-16LE encoded string).

Fix t4041, t7102 and update an older fix in t4205.

Thanks-to: Karsten Blees <blees@dcon.de>
Merge pull request #156 from kasal/test-fix-rev

Fix test suite issues with iso8859-1 parameters