remove legacy legato + duration implementations

[felixroos]

fixes https://github.com/tidalcycles/strudel/issues/111

legato is now doing the same as clip.

this is technically a breaking change because earlier things like

"c d e".legato(.5).note()
// or
note("c d e".legato(.5))

..have worked, now they don't. this would be the working example:

note("c d e").legato(.5)

this is because legato expects the hap value to be an object

edit: the change shouldn't have too big impact because none of the example tunes or the docs show that this is possible

edit: this change should be non breaking if https://github.com/tidalcycles/strudel/pull/973 is added (not sure)