Delete Bootcamp Partition and recover Disk Full Space
The linked method to create a fake Boot Camp partition doesn't work because the former partition is no empty space but an HFS volume (disk0s4). The gpt command won't add partitions in allocated disk space.

To resize your main partition (disk0s2) to the full ~120 GB, boot to your main macOS volume, delete the second HFS+ volume and expand your main partition:

diskutil eraseVolume Free Space disk0s4


Try to expand the main volume:

diskutil resizeVolume disk0s2 R


If the R size option fails try to use a real size like 120g or the percentage 100% (on some external disks this may fail because of some 2 TiB limit).

diskutil resizeVolume disk0s2 120473m


or more exactly:

diskutil resizeVolume disk0s2 120473067520b


or

diskutil resizeVolume disk0s2 100%