Remove back link from 404 error page (#23222967)

I've kept it for 400/403/500/csrffail for now, because they also have a
"try again" link. Yes, both things have browser buttons, but they make
it a *little* clearer to technical users what one could to next, and
especially on csrffail, "step back" is always possible and possibly actually
helpful.

src/pretix/base/modelimport_vouchers.py

@@ -132,7 +132,7 @@ class AllowIgnoreQuotaColumn(BooleanColumnMixin, ImportColumn):
 
 class PriceModeColumn(ImportColumn):
     identifier = 'price_mode'
-    verbose_name = gettext_lazy('Price effect')
+    verbose_name = gettext_lazy('Price mode')
     default_value = None
     initial = 'static:none'
 
@@ -147,7 +147,7 @@ class PriceModeColumn(ImportColumn):
         elif value in reverse:
             return reverse[value]
         else:
-            raise ValidationError(_("Could not parse {value} as a price effect, use one of {options}.").format(
+            raise ValidationError(_("Could not parse {value} as a price mode, use one of {options}.").format(
                 value=value, options=', '.join(d.keys())
             ))
 
@@ -162,7 +162,7 @@ class ValueColumn(DecimalColumnMixin, ImportColumn):
     def clean(self, value, previous_values):
         value = super().clean(value, previous_values)
         if value and previous_values.get("price_mode") == "none":
-            raise ValidationError(_("It is pointless to set a value without a price effect."))
+            raise ValidationError(_("It is pointless to set a value without a price mode."))
         return value
 
     def assign(self, value, obj: Voucher, **kwargs):

src/pretix/base/models/vouchers.py

@@ -239,7 +239,7 @@ class Voucher(LoggedModel):
         )
     )
     price_mode = models.CharField(
-        verbose_name=_("Price effect"),
+        verbose_name=_("Price mode"),
         max_length=100,
         choices=PRICE_MODES,
         default='none'

src/pretix/base/templates/404.html

@@ -8,9 +8,6 @@
         <h1>{% trans "Not found" %}</h1>
         <p>{% trans "I'm afraid we could not find the the resource you requested." %}</p>
         <p>{{ exception }}</p>
-        <p class="links">
-            <a id='goback' href='#'>{% trans "Take a step back" %}</a>
-        </p>
         {% if request.user.is_staff and not staff_session %}
             <form action="{% url 'control:user.sudo' %}?next={{ request.path|add:"?"|add:request.GET.urlencode|urlencode }}" method="post">
                 <p>

src/tests/base/test_modelimport_vouchers.py

@@ -170,7 +170,7 @@ def test_price_mode_validation(event, item, user):
         import_vouchers.apply(
             args=(event.pk, inputfile_factory().id, settings, 'en', user.pk)
         ).get()
-    assert 'It is pointless to set a value without a price effect.' in str(excinfo.value)
+    assert 'It is pointless to set a value without a price mode.' in str(excinfo.value)
 
     settings['price_mode'] = 'static:percent'
     import_vouchers.apply(