Remove deprecated classes and methods

[cqc-alec]

We have a number of formally deprecated classes and methods in pytket. From a quick search these are:

• ClassicalExpBox and friends;
• GlobalisePhasedX;
• SynthesiseUMD;
• NoiseAwarePlacement.modify_config;
• GraphPlacement.modify_config.

So as not to break semver we should make a pytket 2.0 release with these removed. We could consider other small breaking changes at the same time but I would like to minimize the chances of actually breaking people's code, to encourage updating.

At the same time we should probably also make a pytket-1 branch which we can maintain for a certain period with hotfixes.

I suggest we make the 2.0 release in late February.