Remove the styleguide

The idea was that this would be a place to document all the design
patterns used in Notify. However it hasn’t been kept up to date, and,
looking at the `git blame`[1] no new patterns have been added for 5
years.

I think it’s better to get rid of it than have to keep maintaining
something which is inaccurate.

1. 64aa0d359c/app/templates/views/styleguide.html

app/main/views/styleguide.py

@@ -1,40 +0,0 @@
-from flask import abort, current_app, render_template
-from flask_wtf import FlaskForm as Form
-from notifications_utils.template import SMSPreviewTemplate
-from wtforms import (
-    FileField,
-    PasswordField,
-    StringField,
-    TextAreaField,
-    validators,
-)
-
-from app.main import main
-
-
-@main.route('/_styleguide')
-def styleguide():
-
-    if not current_app.config['SHOW_STYLEGUIDE']:
-        abort(404)
-
-    class FormExamples(Form):
-        username = StringField(u'Username')
-        password = PasswordField(u'Password', [validators.required()])
-        code = StringField('Enter code')
-        message = TextAreaField(u'Message')
-        file_upload = FileField('Upload a CSV file to add your recipients’ details')
-
-    sms = "Your vehicle tax for ((registration number)) is due on ((date)). Renew online at www.gov.uk/vehicle-tax"
-
-    form = FormExamples()
-    form.message.data = sms
-    form.validate()
-
-    template = SMSPreviewTemplate({'content': sms, 'template_type': 'sms'})
-
-    return render_template(
-        'views/styleguide.html',
-        form=form,
-        template=template
-    )