[mlir][Toy] Remove unnecessary transpose from chapter 1 example

The call to 'multiply_transpose' in the initialization of the variable 'f' was
intended to have a shape mismatch. However the variable 'a' has shape <2, 3> and
the variable 'c' has shape <3, 2>, so the arguments 'transpose(a)' and 'c' have
in fact compatible shapes (<3, 2> both), the opposite of what is wanted here.
This commit removes the transpose so that arguments 'a' and 'c' have
incompatible shapes <2, 3> and <3, 2>, respectively.

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D151897