Standard & Poor's Corp. yesterday removed Suffolk County. N.Y., from Creditwatch with negative implications and affirmed its BBB rating on about $270 million of the county's uninsured general obligation debt. The rating agency also said, however, that Suffolk's credit outlook "remains negative" because of challenges that county officials face in balancing the county's 1993 fiscal year budget, which begins Jan. 1. In December 1991, Standard & Poor's alerted the investment community that the county's fiscal health had begun to fail when it put Suffolk on Creditwatch. But in recent months, the county pulled itself out of the rating agency's doghouse by taking several steps to stabilize its credit situation, Standard & Poor's said.