removed deprecated sourcemap option

`sourcemaps` has been the preferred option for ages now; cf.
41bacc6

NB: this constitutes a breaking change

Author: moonglum

lib/bundle/config.js

@@ -50,12 +50,7 @@ module.exports = generateConfig;
 function generateConfig({ extensions = [], // eslint-disable-next-line indent
 		externals, format, exports, // eslint-disable-next-line indent
 		esnext, jsx, typescript, // eslint-disable-next-line indent
-		sourcemaps, sourcemap, compact }, { browsers }) {
-	if(sourcemap !== undefined) { // for backwards compatibility (explicit error)
-		abort(`ERROR: ${repr("sourcemap", false)} has been deprecated in ` +
-				`favor of ${repr("sourcemaps", false)}`);
-	}
-
+		sourcemaps, compact }, { browsers }) {
 	let cfg = { sourcemap: sourcemaps };
 	let plugins = [];