Fix an out-of-order execution issue regarding pkg(8):

• pkg(8) cannot be removed before subsequent reinvocations
• The PKG_CACHEDIR cannot be cleaned after the repo*.sqlite has been removed
• pkg(8) cannot be removed as a precursor to any of the other steps involved here

MFC after: 3 days
X-MFC-With: r285722
X-MFC-Before: 10.2-{BETA3,RC1} (whichever happens next)
Sponsored by: The FreeBSD Foundation