Mul.flatten: remove special handling for C.exp thus refactoring o=b**e processing
Since we just reworked exp(x).as_base_exp() to return (E, x) there is no reason
to do special handling of C.exp in Mul.
This allows us to simplify the code, and speed it up a bit:
Timings (cache: off)
--------------------
d = [x,y,z]
%timeit fem_test.py
Mul(*d)
old: 270 µs 5.35 s
new: 253 µs 5.24 s
speedup: 6.7% 2%
Signed-off-by: Kirill Smelkov <kirr@landau.phys.spbu.ru>
Signed-off-by: Ondrej Certik <ondrej@certik.cz>