Is unjailbreaking as simple as removing cydia?

You clearly have done zero research.

No. Jailbreakme does more than "install Cydia" and deleting Cydia doesn't unjailbreak your phone. Go into iTunes and restore, that will remove your JB.

No. To remove a Jailbreak, connect to iTunes and restore. Removing Cydia will do nothing but limit what you can do with your Jailbroken device, and even cause instability

Restore with iTunes and set up as new, if you truly want to delete any traces of the jailbreak. Cydia is just the browser that allows you to install tweaks and apps. Jailbreaking does a lot more behind the scenes that we don't see.

I would suggest researching what a jailbreak is before actually rocking a jailbroken phone. Ignorance will only result in a screwed up phone and endless post about "I bricked my phone, please help".