I found this information on Quora but the link was gross so I am just putting the information here.
To get remove the abomination called Hangouts from gmail
Go to Gmail settings, the gear on the upper right of the Gmail app, and select Settings.
Select the Chat menu, on the far right of the menu options, opposite General.
Turn Chat off, and Save Changes.
I realize this is not a developer thing... but I cannot tell you the amount of joy I felt when I refreshed gmail in my browser and the ugly Hangout list in the left corner went away.