Remove shape function (duplicate of size)

[JakobAsslaender]

Hi everyone,

so sorry, I just realized that you prefer opening an issue instead of a PR (which I had already done #297). Anyways, here is the issue and I would be grateful for your feedback!

We have encountered in several of our packages a conflict between the functions LinearOperators.shape and Distributions.shape (JuliaImageRecon/LinearOperatorCollection.jl#3 (comment)). Since the former is a duplicate of size, I was wondering if it would be feasible to drop shape from this package. To make everyone's life easier, I put those changes in a PR (#297).

Many thanks for considering!

[dpo]

Sorry for the slow reply and thank you for the pull request. CI is running now.