cdm/src/main/java/ucar/ma2/Index.java
Index reduce() {
    Index c = this;
    for (int ii = 0; ii < rank; ii++)
      if (shape[ii] == 1) {  // do this on the first one you find
        Index newc = c.reduce(ii);
        return newc.reduce();  // any more to do?
      }
    return c;
  }
Index reduce() {
    Index c = this;
    for (int ii = 0; ii < rank; ii++)
      if (shape[ii] == 1) {  // do this on the first one you find
        Index newc = c.reduce(ii);
        return newc.reduce();  // any more to do?
      }
    return c;
  }
Create a new Index based on current one by
eliminating any dimensions with length one.

@return the new Index