Removing free partition on Macbook Macintosh HD
You a not suppose to remove the EFI partition. This partition was created when macOS was installed. To remove the Ubuntu files from the FA32 formatted volume stored in this partition, take the following steps.

Note: I realize, it is to late for you to follow these steps. I post the steps for others who may have the same question.


Boot to macOS and open a Terminal application window.

Enter the command below to mount the volume stored in the EFI partition. This volume will have the name EFI.
sudo diskutil mount disk0s1


Use the Finder application to remove the EFI/BOOT and EFI/ubuntu folders from the EFI volume.

Enter the command below to unmount the volume stored in the EFI partition.
diskutil unmount disk0s1