remove debian_version variable

replaced with the corresponding ansible fact

texlive/tasks/main.yml

@@ -55,7 +55,7 @@
   apt: name={{ item }} state=latest install_recommends=no
   with_items:
     - fonts-droid 
-  when: debian_version == "jessie"
+  when: ansible_distribution_release == "jessie"
   tags:
     - texlive
     - packages
@@ -64,7 +64,7 @@
   apt: name={{ item }} state=latest install_recommends=no
   with_items:
     - fonts-droid-fallback
-  when: debian_version == "stretch"
+  when: ansible_distribution_release == "stretch"
   tags:
     - texlive
     - packages