Task: My all worked done from Gmail app. Sign out the Gmail account
Steps:
Go back to the previous screen
Click on the Manage your Google Account in the Account section
Click on the drop down arrow next to the thomas.blanc1978@gmail.com
Click on the Manage accounts on this device 
Scroll down to view more account
Click on my gmail account thomas.blanc1978@gmail.com
Click on the Remove account button
Click on the Remove account next to Cancel