Remove check of optimize arg

[h-larsson]

a = np.arange(60.).reshape(3,4,5)
b = np.arange(24.).reshape(4,3,2)
np.einsum('ijk,jil->kl', a, b, optimize=("optimal",200))
path = np.einsum_path('ijk,ilm,njm,nlk,abc->',a,a,a,a,a,optimize='optimal')[0]
np.einsum('ijk,ilm,njm,nlk,abc->',a,a,a,a,a, optimize=path)

are both valid options. This seems to be supported by the implementation of einsum_path in pytblis, which checks the keyword argument.

[chillenb]

Thanks for the PR!

I was going to ask about the whitespace but then you fixed it immediately, lol.