models: Delete unused function get_realm_outgoing_webhook_services_name.
models: Delete unused function get_realm_outgoing_webhook_services_name.

This was implemented as part of some preparatory work for outgoing
webhooks, but isn't actually used.

eeshangarg/zulip,timabbott/zulip,synicalsyntax/zulip,dhcrzf/zulip,zulip/zulip,timabbott/zulip,jackrzhang/zulip,zulip/zulip,kou/zulip,shubhamdhama/zulip,rht/zulip,timabbott/zulip,timabbott/zulip,kou/zulip,jackrzhang/zulip,brainwane/zulip,synicalsyntax/zulip,zulip/zulip,zulip/zulip,tommyip/zulip,tommyip/zulip,brainwane/zulip,andersk/zulip,zulip/zulip,hackerkid/zulip,zulip/zulip,tommyip/zulip,punchagan/zulip,timabbott/zulip,jackrzhang/zulip,showell/zulip,rishig/zulip,jackrzhang/zulip,hackerkid/zulip,rishig/zulip,jackrzhang/zulip,andersk/zulip,brainwane/zulip,showell/zulip,shubhamdhama/zulip,dhcrzf/zulip,timabbott/zulip,rht/zulip,rht/zulip,punchagan/zulip,hackerkid/zulip,synicalsyntax/zulip,rishig/zulip,hackerkid/zulip,showell/zulip,shubhamdhama/zulip,brainwane/zulip,hackerkid/zulip,rht/zulip,rht/zulip,showell/zulip,eeshangarg/zulip,synicalsyntax/zulip,kou/zulip,andersk/zulip,andersk/zulip,shubhamdhama/zulip,eeshangarg/zulip,jackrzhang/zulip,timabbott/zulip,synicalsyntax/zulip,hackerkid/zulip,tommyip/zulip,shubhamdhama/zulip,eeshangarg/zulip,synicalsyntax/zulip,rishig/zulip,eeshangarg/zulip,eeshangarg/zulip,rishig/zulip,synicalsyntax/zulip,punchagan/zulip,tommyip/zulip,showell/zulip,rht/zulip,tommyip/zulip,punchagan/zulip,andersk/zulip,punchagan/zulip,showell/zulip,brainwane/zulip,andersk/zulip,dhcrzf/zulip,tommyip/zulip,showell/zulip,shubhamdhama/zulip,jackrzhang/zulip,kou/zulip,andersk/zulip,brainwane/zulip,dhcrzf/zulip,rishig/zulip,punchagan/zulip,rishig/zulip,dhcrzf/zulip,kou/zulip,dhcrzf/zulip,hackerkid/zulip,eeshangarg/zulip,punchagan/zulip,brainwane/zulip,kou/zulip,rht/zulip,zulip/zulip,dhcrzf/zulip,shubhamdhama/zulip,kou/zulip