Fix assert message to avoid printing garbage

Fix assert message to avoid printing garbage

Fix an off by one error in assert() to avoid printing garbage
characters to the log. Remove the newline character generated by
ctime() to match the format generated by the other logging functions.

FIXES 124613

Reviewed-on: http://gerrit.openafs.org/102
Verified-by: Russ Allbery <rra@stanford.edu>
Reviewed-by: Russ Allbery <rra@stanford.edu>