wendelin: Unpin wendelin.core from versions in -dev variant

This is required so that buildout does not fallback to installing
non-dev egg if version of wendelin.core from -dev differs from what has
been pinned.

For example the following

    [buildout]
    extends =
      https://lab.node.vifib.com/nexedi/slapos/raw/1.0.12/software/wendelin/software-dev.cfg

    # pin wendelin.core-dev to latest assumed-good revision with ZBlk1 support
    [wendelin.core-repository]
    revision = c507d9009f59fec2041bac9c31c5b08a48d3897d

will install wendelin.core-0.4.egg from pypi instead of installing
c507d9009f59fec2041bac9c31c5b08a48d3897d from repository, because that
latter revision says it is already version 0.5 and 1.0.12 wendelin SR
pins wendelin.core to 0.4 .

So unpin wendelin.core from versions and let software-dev.cfg work
always.

/cc @klaus
/reviewed-by @Tyagov  (on !36)

software/wendelin/software-dev.cfg

@@ -11,3 +11,10 @@ parts += wendelin.core-dev
 # tell erp5 to use -dev eggs instead of released ones
 eggs -= ${wendelin.core:egg}
 eggs += ${wendelin.core-dev:egg}
+
+
+# unpin wendelin.core from versions, so that if there is difference between
+# version of wendelin.core-dev and what was pinned, buildout does not fallback
+# to installing non-dev egg
+[versions]
+wendelin.core =