Cfrgtkky

I recently updated from Ubuntu 16.04 to 18.04.
I had separate partitions for / and home, and for the update I made a clean install over the / folder, so that I saved everything in the home folder, while the rest was formatted.
After the update, I only had python 3.6.7, which as I understand is the default version for the operative system. Then, I installed python 2.7 (version 2.7.15rc1, specifically), so I was expecting to have only these two versions installed.

1) Am I correct in saying that the 3.6.7 is the default version for Ubuntu 18.04? So, no matter what, this version is needed from the system, and should not be uninstalled?

2) As I said, I was expecting to have only python 3.6.7 and 2.7.15rc1 installed. However, after a search, I found these files:

/snap/core/6130/usr/bin/python3.5: Python 3.5.2

/snap/core/6130/usr/bin/python3.5m: Python 3.5.2

/snap/core/6259/usr/bin/python3.5: Python 3.5.2

/snap/core/6259/usr/bin/python3.5m: Python 3.5.2

/snap/core/6350/usr/bin/python3.5: Python 3.5.2

/snap/core/6350/usr/bin/python3.5m: Python 3.5.2

are they relics from before the update? Are they system files? Can they be removed, and how?
I don't understand what these folders contain, since as I said I formatted the / partition.
If I give the command:

snap list

I get:

Name                  Version                 Rev   Tracking  Publisher   Notes

core                  16-2.37.1               6350  stable    canonical✓  core

gnome-3-26-1604       3.26.0                  74    stable/…  canonical✓  -

gnome-calculator      3.30.1                  260   stable/…  canonical✓  -

gnome-characters      3.30.0                  139   stable/…  canonical✓  -

gnome-logs            3.30.0                  45    stable/…  canonical✓  -

gnome-system-monitor  3.30.0                  57    stable/…  canonical✓  -

gtk-common-themes     0.1-4-g88bc1b2          818   stable/…  canonical✓  -

skype                 8.34.0.78               66    stable    skype✓      classic

spotify               1.0.98.78.gb45d2a6b-10  31    stable    spotify✓    -

vlc                   3.0.6                   770   stable    videolan✓   -

which are the programs I installed from the software center after the update to 18.04.

3) If I use the command:

whereis pip

I get the output

/home/carlo/.local/bin/pip /home/carlo/.local/bin/pip2.7

which is almost surely from before the update (I did not delete the /home partition when updating to Ubuntu18.04).
But how can I uninstall it?

If I try:

sudo apt-get remove python-pip

I obtain the result (something like this, my system is in Italian, I'm translating):

"python-pip" is not installed and cannot be removed

so, apt.-get is not finding the version of pip I want to remove from the /home folder. Same goes when using Synaptic, python-pip results not to be installed. How do I remove it?

Thanks in advance!