fix #631 on the control of the resolution-dependent fast algorithm and clean-up
With fix in #631, SBT is always tested in RDO, as "((cu->lwidth() > 32 || cu->lheight() > 32) && !(m_pcEncCfg->getUse64SBTRDOCheck()))
" is always false.
Actually, it should be skipped for CU with one side > 32 when the picture resolution is below HD, as described by the resolution-dependent fast algorithm in JVET-P0983 method 1.
To make the command line name more accurate, it was changed from "SBT64RDO" to "SBTFast64".