[native] move navigate to emoji user avatar creation function to be within edit user avatar

Summary:
Small cleanup diff, I figured it would be better to have this logic within EditUserAvatar than in the ProfileScreen

Depends on D7621

Test Plan: flow still able to navigate to the user emoji avatar creation screen

Reviewers: ashoat, atul

Reviewed By: ashoat

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D7622