dygraphs v2.2.1

we don’t use ES6 Symbol() anywhere

fixes tests/unboxed-spark

via tests/exported-symbols

(mostly ours but also jQuery’s)

+ small fixes while here

Same as PR#953 fixed for the gallery, really.

now we don’t ship that any more, as we can test the Debian-built
code (.js and .min.js both) using an NPM-built tests.js on NPM

from commit a17153e7

these here actually do not use `this`, AFAICT