dependencies: remove capstone

[jsiverskog]

the implementation already supports that capstone may not be installed. capstone is somewhat slow to install on some platforms (e.g. raspberry pi), and not always needed.

[ithinuel]

Hello, Thank you for the contribution.

As I understand this, this is a matter of weighing the benefit for people using this step command and relying on it printing the asm versus people installing pyocd from pip on "slow" systems.

I don't personally have an opinion on that matter and don't feel legitimate to make the call on this.

[carlosperate]

Not indicating if this should be removed or kept in install_requires, but just to add a small comment that:
if it is going to be removed from install_requires it might be better if it goes into a different extras_require.
Maybe a new one, like pemicro? and maybe at that point it'd be good as well to add a third called all to include all options.
On top of that it would also be good to update all the documentation indicating how to install the different dependencies.

Of course, it's understandable not wanting to do the extra work without first knowing if a PR is going to be accepted, I just wanted to point this out to have it in consideration as well.