code: function cleanTables(ttf) {
              delete ttf.readOptions;
              delete ttf.tables;
              delete ttf.hmtx;
              delete ttf.loca;
              if (ttf.post) {
                  delete ttf.post.nameIndex;
                  delete ttf.post.names;
              }
  
              delete ttf.subsetMap;
  
              // 不携带hinting信息则删除hint相关表
              if (!this.options.hinting) {
                  delete ttf.fpgm;
                  delete ttf.cvt;
                  delete ttf.prep;
  
                  ttf.glyf.forEach(function (glyf) {
                      delete glyf.instructions;
                  });
              }
  
              // 复合字形转简单字形
              if (this.options.compound2simple && ttf.maxp.maxComponentElements) {
                  ttf.glyf.forEach(function (glyf, index) {
                      if (glyf.compound) {
                          compound2simpleglyf(index, ttf, true);
                      }
                  });
                  ttf.maxp.maxComponentElements = 0;
                  ttf.maxp.maxComponentDepth = 0;
              }
          }
docs: 清除非必须的表
  @param {Object} ttf ttf对象