Simplify getPackagePath() to use the builtin node package resolver only

Instead of going through the rollup plugin. Turns out the rollup plugin
api shouldn't be used outside of rollup.

Ideally this should give us the same path resolution anyway, even though it's
potentially a different implementation.

rollup.utils.js

@@ -2,7 +2,6 @@ import path from 'path';
 import url from 'url';
 import fs from 'fs';
 import child_process from 'child_process';
-import resolve from '@rollup/plugin-node-resolve';
 import selfsigned from 'selfsigned';
 import findCacheDir from 'find-cache-dir';
 
@@ -31,24 +30,14 @@ export async function getDistPath(packageName, assetPath) {
 }
 
 export async function getPackagePath(packageName, assetPath) {
-    const r = resolve();
-    // XXX: https://gitlab.tugraz.at/dbp/web-components/toolkit/-/issues/57
-    r.resolve = () => { return null; };
-    const resolved = await r.resolveId(packageName);
     let packageRoot;
-    if (resolved !== null) {
-        const id = (await r.resolveId(packageName)).id;
-        const packageInfo = r.getPackageInfoForId(id);
-        packageRoot = packageInfo.root;
+    let current = require.resolve('./package.json');
+    if (require(current).name === packageName) {
+        // current package
+        packageRoot = path.dirname(current);
     } else {
-        let current = require.resolve('./package.json');
-        if (require(current).name === packageName) {
-            // current package
-            packageRoot = path.dirname(current);
-        } else {
-            // Non JS packages
-            packageRoot = path.dirname(require.resolve(packageName + '/package.json'));
-        }
+        // Other packages from nodes_modules etc.
+        packageRoot = path.dirname(require.resolve(packageName + '/package.json'));
     }
     return path.relative(process.cwd(), path.join(packageRoot, assetPath));
 }