treewide: Get rid of most parseDrvName without breaking compat

That is because this commit should be merged to both master and
release-19.09.

doc/configuration.xml

@@ -179,11 +179,10 @@
      allows unfree packages named flash player and visual studio code:
 <programlisting>
 {
-  allowUnfreePredicate = (pkg: builtins.elem
-    (builtins.parseDrvName pkg.name).name [
-      "flashplayer"
-      "vscode"
-    ]);
+  allowUnfreePredicate = pkg: builtins.elem (lib.getName pkg) [
+    "flashplayer"
+    "vscode"
+  ];
 }
 </programlisting>
     </para>
@@ -273,7 +272,7 @@
      very short names:
 <programlisting>
 {
-  allowInsecurePredicate = (pkg: (builtins.stringLength (builtins.parseDrvName pkg.name).name) &lt;= 5);
+  allowInsecurePredicate = (pkg: (builtins.stringLength (lib.getName pkg) &lt;= 5);
 }
 </programlisting>
     </para>