Fix tsconfig to emit JS files in addition to declarations (#470)

`tsconfig.build.json` is now instructing TypeScript to only emit type
declaration files instead of also emitting JavaScript files. This change
was erroneously made in a previous commit. This commit removes that
instruction.

tsconfig.build.json

@@ -2,7 +2,6 @@
   "extends": "./tsconfig.json",
   "compilerOptions": {
     "declaration": true,
-    "emitDeclarationOnly": true,
     "inlineSources": true,
     "noEmit": false,
     "outDir": "dist",