make: fix echoing of command with '-' in silent target in jobs mode

Since job.c 1.83 from 2003-12-20, the command had been echoed even if
the target had the attribute '.SILENT'.

In sh-flags.exp, each removed 'echo' command is below a target name
matching the pattern 'opt-?j????-tgt-??s-cmd-?i?', which means that the
target was marked as silent, either through a global '.SILENT'
declaration or the command line option '-s' or the attribute '.SILENT'
on the target.

Reported by Alan Barrett in PR#45356.

(rillig)