Get rid of console.log statements

[pdehaan]

Current status:

$ npm run lint

...

> firefox-send@0.2.0 lint:js /home/ubuntu/send
> eslint .


/home/ubuntu/send/frontend/src/download.js
  105:9  warning  Unexpected console statement  no-console
  156:9  warning  Unexpected console statement  no-console

/home/ubuntu/send/frontend/src/fileSender.js
  29:11  warning  Unexpected console statement  no-console
  31:11  warning  Unexpected console statement  no-console
  57:11  warning  Unexpected console statement  no-console

/home/ubuntu/send/frontend/src/upload.js
  212:9   warning  Unexpected console statement  no-console
  224:9   warning  Unexpected console statement  no-console
  300:11  warning  Unexpected console statement  no-console

✖ 8 problems (0 errors, 8 warnings)

We should either remove all unnecessary console.log() statements (and/or ESLint ignore any valid ones), or possibly just remove the ESLint rule to avoid console vomit in Circle-CI and when linting locally.

[pdehaan]

Ref: #281 wherein I disabled the no-console rule in the test/ directory, and reduced the warnings to 16.