Remove console.log.bind(console) pattern in log.js

[bgrins]

I filed https://bugzilla.mozilla.org/show_bug.cgi?id=1445772 to handle other cases in m-c. We don't need to manually bind console methods to the console object anymore as of Bug
989619.

So we should be able to simplify these:

screenshots/addon/webextension/log.js

Lines 30 to 44 in 9e4ca4e

	if (shouldLog.debug) {
	exports.debug = console.debug.bind(console);
	}
	if (shouldLog.info) {
	exports.info = console.info.bind(console);
	}
	if (shouldLog.warn) {
	exports.warn = console.warn.bind(console);
	}
	if (shouldLog.error) {
	exports.error = console.error.bind(console);
	}

to exports.debug = console.debug, etc.

[bgrins]

Also, Console.jsm is imported but doesn't seem to be used:

screenshots/addon/bootstrap.js

Lines 15 to 16 in dd44303

	ChromeUtils.defineModuleGetter(this, "Console",
	"resource://gre/modules/Console.jsm");

. Removing that reference will help with Console.jsm removal (https://bugzilla.mozilla.org/show_bug.cgi?id=1430810)