OPINION: Senate Minority Leader Charles E. Schumer should take heed: Even NPR’s sugar daddy has cut the purse strings. Enough is enough for the Corporation for Public Broadcasting , which for decades has been the most vocal defender of forced taxpayer subsidies for National Public Radio . CPB’s support has ended with the kind of dramatic abruptness that would make Shakespeare stand in awe. Late last month, CPB reversed course and canceled a $30 million grant for NPR to operate the Public Radio