#74 and #126 Remove "exception_to" from licenses metadata

 * the rationale is that an exception can aplly to many different
   licenses and there is no way to enforce this sanely and consistently.
 * instead and to support fully license expression in #74 exceptions
   will be treated with a flag "is_exception" that tags them as
   exception. This can then be used by the license_expression library
   to enforce the validty of expressions thoughout.

Signed-off-by: Philippe Ombredanne <pombredanne@nexb.com>

src/licensedcode/data/licenses/lgpl-2.0-fltk.yml

@@ -3,5 +3,4 @@ short_name: FLTK LGPL exception
 name: FLTK LGPL exception
 category: Copyleft Limited
 owner: Fast Light Toolkit
-exception_to: lgpl-2.0
 homepage_url: http://www.fltk.org/COPYING.php

src/licensedcode/data/licenses/lgpl-2.1-nokia-qt-1.0.yml

@@ -3,6 +3,5 @@ short_name: Nokia Qt LGPL Exception 1.0
 name: Nokia Qt LGPL Exception v1.0
 category: Copyleft Limited
 owner: Nokia
-exception_to: lgpl-2.1
 notes: the 5% limit in this license is quite impractical.
  This exception is exactly the same as a the The Qt Company Qt LGPL Exception v1.1

src/licensedcode/data/licenses/lgpl-2.1-plus-linking.yml

@@ -3,6 +3,5 @@ short_name: LGPL linking exception
 name: LGPL linking exception
 category: Copyleft Limited
 owner: Free Software Foundation (FSF)
-exception_to: lgpl-2.1
 text_urls:
     - http://sources.redhat.com/git/gitweb.cgi?p=glibc.git;a=blob;f=libio/libio.h

src/licensedcode/data/licenses/sencha-app-floss-exception.yml

@@ -8,4 +8,3 @@ other_urls:
     - http://www.sencha.com/legal/open-source-faq/open-source-license-exception-for-applications/
     - http://web.archive.org/web/20140816133327/http://www.sencha.com/legal/open-source-faq/open-source-license-exception-for-applications/
 notes: Sencha stopped offering this exception in 2015.
-exception_to: gpl-3.0

src/licensedcode/data/licenses/sencha-dev-floss-exception.yml

@@ -8,4 +8,3 @@ other_urls:
     - http://www.sencha.com/legal/open-source-faq/open-source-license-exception-for-development/
     - http://web.archive.org/web/20140816133230/http://www.sencha.com/legal/open-source-faq/open-source-license-exception-for-development/
 notes: Sencha stopped offering this exception in 2015.
-exception_to: gpl-3.0