remove Emitter emit1, emit2, emit3

[pixelzoom]

In light of work like phetsims/scenery#928 and #211 ...

Emitter emit1, emit2, and emit3 should be deleted. They are all deprecated. @samreid recently changed their implementations to be nearly identical and call emit, see 880b311. And they would be relatively easy to replace with emit using global string replacement.

Occurrences:
70 emit1
9 emit2
6 emit3

Assigning to @ariel-phet to prioritize and assign.

[samreid]

The reason I didn't just tackle this as part of #211 was that emit requires validators whereas emit1,2,3 ignore validation. So we have these kind of options:

a) add a (temporary?) feature to Emitter that ignores validation
b) use validators like [Any] for emit1, [Any,Any] for emit2 etc.
c) add the correct validators for each Emitter as part of this port.

(c) is the preferable long term solution, but it would be nice to shape up the Emitter validator API first, as decided in #204 (comment)

Also self assigning this for further consideration, or in case I figure a simple way to address these 80+ cases.

[zepumph]

duplicate of #211