ALBANY - State GOP Chairman Stephen Minarik, who just knocked William Weld out of the race for governor, will now try to do the same with Republican Senate hopeful Katherine "KT" McFarland, The Post has learned. Minarik, backed by other GOP leaders, will publicly urge McFarland, a Reagan-era Pentagon official, to drop out of the Senate race today "in the interest of party unity," a source familiar with Minarik's thinking said. Minarik will urge GOP voters to rally around former Yonkers Mayor John Spencer, who defeated McFarland, 63 percent to 36 percent, at last week's party nominating convention, as the...