nav: Remove unused component SidebarRow.
nav: Remove unused component SidebarRow.

This has been dead since 81c2cfe73 "Remove outdated 'main-tabbed' UI",
in mid-2017.

vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile