Remove extraneous pcre BuildRequires
    
    The pcre BR was added in 6dc6285 ("Improve test suite coverage",
    2017-11-10), which seems to have been an oversight.  The test suite
    improvements were worked on over a long period of time.  It is quite
    likely that the pcre BR was needed before 6dc6285 was finalized.
    Regardless, we began building against pcre2 in 595b682 ("Use pcre2
    library", 2017-07-22).
    
    Note that pcre remains in the minimal buildroot due to dependencies in
    glib2 and grep.