settings: Remove language_modal_elem from user_settings_panel.
settings: Remove language_modal_elem from user_settings_panel.

We added language_modal_elem to settings_display.user_settings_panel
object considering there would be realm-level default_language
setting and we would need to access the modal element using a
variable to avoid code duplication. But now we have decided that
we do not want the setting and we would instead use browser's
language to set the language for new user, so now we do not need
this variable and we can instead use id of the modal directly.

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