Cleanup Default Wiki Pages for 0.11

[ilias@…]

As an example, the document:

source:trunk/trac/wiki/default-pages/TracInterfaceCustomization@4819​

A newly created trac 0.11 environment will contain the above default wiki page.

But this page contains an unnecessary entry which refers to trac 0.9:

 Note: in projects created with a Trac version prior to 0.9 you will need
 to create this folder.

This text (and similar text across the documentation contained in the wiki default pages) should be removed, thus a newly created 0.11 environment contains concise documentation which refers to the actual version 0.11.

[Christian Boos]

Please follow-up in #4716.