refactor: remove unused Pillow

requirements.txt

@@ -1,19 +1,16 @@
 Django==2.1.11
-Pillow==2.6.1
 Unipath==1.1
 coverage==4.5.1
 django-appconf==1.0.2
 django-cors-headers==2.4.0
 django-discover-runner==1.0
-django-imagekit==4.0.2
 django-redis==4.10.0
 django-cachalot==2.1.0
 django-tastypie==0.14.2
 djangorestframework==3.9.0
 drf-ujson==1.2.0
 gunicorn==19.9.0
 mimeparse==0.1.3
-pilkit==2.0
 psycopg2==2.7.5
 python-dateutil==2.7.3
 python-mimeparse==1.6.0