t4108: replace create_file with test_write_lines

t4108: replace create_file with test_write_lines

Since the locally defined create_file() duplicates the functionality of
the test_write_lines() helper function, remove create_file() and replace
all instances with test_write_lines(). While we're at it, move
redirection operators to the end of the command which is the more
conventional place to put it.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>