actions: Fix type-incorrect custom profile field value assignment.
actions: Fix type-incorrect custom profile field value assignment.

The old assignment is incorrect - field_value.value is a TextField() and
should always be a string. This didn't strictly break anything, because
django converts the value to a string when .save()ing to the db, but
field_value.value persists as a non-string for the rest of this
codepath. After fixing this, the small codeblock in
notify_user_update_custom_profile_data handling conversion of
field_value.value to a string becomes redundant.

We're assured that we're not breaking event format by the test
test_custom_profile_field_data_events in test_events.py.

zulip/zulip,kou/zulip,eeshangarg/zulip,zulip/zulip,andersk/zulip,eeshangarg/zulip,kou/zulip,rht/zulip,zulip/zulip,eeshangarg/zulip,kou/zulip,andersk/zulip,andersk/zulip,andersk/zulip,andersk/zulip,rht/zulip,eeshangarg/zulip,kou/zulip,zulip/zulip,kou/zulip,rht/zulip,rht/zulip,kou/zulip,rht/zulip,zulip/zulip,rht/zulip,zulip/zulip,kou/zulip,andersk/zulip,zulip/zulip,eeshangarg/zulip,eeshangarg/zulip,andersk/zulip,eeshangarg/zulip,rht/zulip