Remove obsolete sparc64 stanza. This collided with ONLY_FOR_ARCHS
statements in the ports that include it, with the following absurd
value for IGNORE on e.g. aarch64:

is only for amd64 i386, while you are running aarch64 (reason: Clover needs a GPU supported by the Radeon KMS driver) (reason: not supported on sparc64)

Approved by: portmgr (tier-2 blanket)