Do not force targets to be SECONDARY

Do not force targets to be SECONDARY

In SV 43677 we forced targets to be secondary if we found an
intermediate file that was listed as a prerequisite of another
target.  This overrides .INTERMEDIATE settings, so doesn't work.
Now that we have an is_explicit flag in targets, use that instead.

* src/implicit.c (pattern_search): Remove setting of secondary.
Preserve the value of the is_explicit flag when creating a new
file target, and consider it when setting the intermediate flag.
* tests/scripts/features/patternrules: Add a test w/out INTERMEDIATE
* tests/scripts/targets/INTERMEDIATE: Add a test with INTERMEDIATE