rpmcliSign() only creates or deletes signatures

rpmcliSign() only creates or deletes signatures
- Lose the "this has got something to do with signatures and stuff"
  dispatcher mode, rpmcliSign() now only does what it says. It also
  doesn't need transaction set for anything. It doesn't need much
  else than files to operate on, what to do and possibly a passphrase.
  It probably will need more when rpmLookupSignatureType()
  is put out of its misery, but this'll do for now.
- Lose the now unnecessary passPhrase member from QVA_t