dashboard: remove unused store_tags file

circle/dashboard/templatetags/store_tags.py

-from datetime import datetime
-
-from django import template
-from django.utils.timesince import timesince
-
-register = template.Library()
-
-
-@register.simple_tag(name="bytes_to_megabytes")
-def bytes_to_megabytes(size):
-    if size:
-        return size / (1024 * 1024)
-    else:
-        return 0
-
-
-@register.simple_tag(name="timestamp_to_date")
-def timestamp_to_date(timestamp):
-    date = datetime.fromtimestamp(float(timestamp))
-    if (datetime.now() - date).days < 1:
-        date = timesince(date)
-    return date