[bug#60763] [PATCH] tests: change `sort|uniq` to `sort -u`

[Karl Berry]

    -    done | sed 's,^\./,,' | sort | uniq >$(am__tfs); \
    +    done | sed 's,^\./,,' | sort -u >$(am__tfs); \

Sure, looks good, please commit. (60764 looks like a dup?)