Bug 13204: Plugin housekeeping: Remove labs_theses.pl plugin

Bug 13204: Plugin housekeeping: Remove labs_theses.pl plugin

As it seems, this plugin has been created for UNIMARC field 328
(Dissertation note). It refers to authval category LABTHE.

The plugin seems however not to be used: it contains several critical errors.
I tried a quick fix but it was not good enough. Since the code can be
recovered from git (if needed), a real fix can always follow this patch.

What are some problems:
[1] The path to the template is wrong. Should be cataloguing/value_builder
[2] The plugin parameter $input is not used. A new CGI object is created.
[3] Resolving errors 1 and 2 still results in premature end of script
    headers.
[4] Not sure whether the plugin can effectively handle missing LABTHE values.

Instead of keeping this in Koha, I opt for removing it for now. As additional
argument I would mention that labs_theses does not have Focus or Blur actions,
only the Click action that does not work.

Test plan:
Git grep on labs_theses.

Signed-off-by: Frederic Demians <f.demians@tamil.fr>
This antique plugin deserves to live forever in Git Historical Museum.

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>
Small fix so the patch applies.