patchtest: reduce checksum test output length

patchtest: reduce checksum test output length

The test_lic_files_chksum_modified_not_mentioned test in TestMetadata is
outputting very long lines that fail the maximum length check when
sending email results, preventing the actual errors from being
displayed. Reduce the length of the failure message by rewording and
removing redundant information.

Signed-off-by: Trevor Gamblin <tgamblin@baylibre.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>