Remove Python 2.7 FileNotFoundError compatibility shims

[rtibbles]

Summary

Since Python 2.7 is no longer supported, remove all instances of the FileNotFoundError compatibility shim that was used to map FileNotFoundError to IOError for Python 2.7 compatibility.

Modified files:

• kolibri/utils/file_transfer.py
• kolibri/utils/filesystem.py
• kolibri/utils/server.py
• kolibri/core/content/utils/content_manifest.py

References

Final bit of Python 2.7 compatibility code, should close #13882

Reviewer guidance

Are there any other instances of this that have been missed? Any other Python 2.7 compatibility things still extant in the codebase?

:robot: This was created by Claude Code. @rtibbles then reviewed the generated output, and did iterative rounds of updates before making it ready for review :robot:

[github-actions[bot]]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.19.0b2.dev0_git.96.gcc8e431c.pex
Windows Installer (EXE)	kolibri-0.19.0b2.dev0+git.96.gcc8e431c-windows-setup-unsigned.exe
Debian Package	kolibri_0.19.0b2.dev0+git.96.gcc8e431c-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.19.0b2.dev0+git.96.gcc8e431c.dmg
Android Package (APK)	kolibri-0.19.0b2.dev0+git.96.gcc8e431c-0.1.6-debug.apk
Raspberry Pi Image	kolibri-pi-image-0.19.0b2.dev0+git.96.gcc8e431c.zip
TAR file	kolibri-0.19.0b2.dev0+git.96.gcc8e431c.tar.gz
WHL file	kolibri-0.19.0b2.dev0+git.96.gcc8e431c-py2.py3-none-any.whl