eja: alter BilinearFormEJA to take only a matrix argument.

The BilinearFormEJA constructor originally took both the size "n" and
a bilinear form matrix "B" that acted on the x-bar component of an
algebra element. This was a bit silly: except when n=0, we can
determine the size of the algebra from the bilinear form matrix.

Now, we insist that the entire matrix "B" be passed in, including the
upper-left "1" block. This allows us to pass in a matrix of size zero
to get the trivial algebra, and in all other cases, to infer that the
dimension of the algebra is the size of the matrix.