remove redundant typings when using interfaces

[alexrudd2]

One thing that'd be nice to look at is unnecessary typings, but I don't know if those tools have rules for that. For example in server.ts we define an interface for the Plotter object here:

saxi/src/server.ts

Lines 158 to 163 in d05fc4c

	interface Plotter {
	prePlot: (initialPenHeight: number) => Promise<void>;
	executeMotion: (m: Motion, progress: [number, number]) => Promise<void>;
	postCancel: (initialPenHeight: number) => Promise<void>;
	postPlot: () => Promise<void>;
	}

But the functions below still have their typings :

saxi/src/server.ts

Line 173 in d05fc4c

async postCancel(initialPenHeight: number): Promise<void> {

which hurts the readability in my opinion.

Originally posted by @drskullster in #168 (comment)