Can't reclaim empty space on main macOS partition [macOS Mojave]
You need to first remove the second EFI partition. Enter the commands given below.
diskutil erasevolume free none disk0s3
diskutil apfs resizeContainer disk0s2 0

Explanation:
The disk0s3 slice occurs after the disk0s2 slice. The free space exists after the disk0s3 slice. The command diskutil erasevolume free none disk0s3 will remove the disk0s3 slice from the partition table, thus increase the size of the free space. The diskutil apfs resizeContainer disk0s2 0 command can then be used to add the free space to the disk0s2 slice. In other words, disk0s3 is in the way and is preventing you from adding the free space to disk0s2.