t6000lib: re-fix tr portability
t6000lib: re-fix tr portability

It seems that some implementations of tr don't like a
replacement string of '-----...'; they try to find the
double-dash option "---...".

Instead of this pipeline of tr and sed invocations, just use a
single perl invocation.

Signed-off-by: Jeff King <696e3fbcf235d40b6ea1ebd61c87cbea79d444e7@peff.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git