Revert "xbps-rindex: [sign] pubkey buffer must be kept until index-meta is externalized too."

This reverts commit cbe05bd0f4a07c0fcd451c1dc2485bd35b7fb445.
Revert "xbps-rindex: [sign] free pubkey data obj after externalizing index-meta."

This reverts commit 11e04685ef61116e3e1fe0552d8abfdc4ec5b5b4.
xbps-remove: make -O also remove signature files and skip pkgs with unmatched arch.