Remove unused dependency

We used this for code highlighting when we had documentation in the
admin app.

app/__init__.py

@@ -35,9 +35,6 @@ from notifications_utils.recipients import (
     format_phone_number_human_readable,
 )
 from notifications_utils.formatters import formatted_list
-from pygments import highlight
-from pygments.formatters.html import HtmlFormatter
-from pygments.lexers.javascript import JavascriptLexer
 from werkzeug.exceptions import abort
 from werkzeug.local import LocalProxy
 

requirements.txt

@@ -7,7 +7,6 @@ Flask-Login==0.3.2
 
 credstash==1.8.0
 boto3==1.4.4
-Pygments==2.0.2
 py-gfm==0.1.2
 blinker==1.4
 lxml==3.6.0