Fix expand tests when releasing plugin

Trying to release the plugin after changes for NXBT-2775, the test-expand fails with the following comparison error:

-org.nuxeo.build:test-expand:2.1.2-SNAPSHOT:pom::
+org.nuxeo.build:test-expand:2.1.2:pom::

This is linked to the fact that the "2.1.2-SNAPSHOT" is hardcoded on file src/it/test-expand/dependency-tree.expected
https://github.com/nuxeo/ant-assembly-maven-plugin/commit/4f3d9840236ab4c8608a8cf304b446c64c5b8e0b#diff-228fbc9a3cafb8b593b3233e263d4028R1

There is mechanism to update this as a variable but it's supposed to happen on the src/it/test-expand/dependency-tree.template file, so the "expected" one should not be commited but recreated thanks to the template.