No `pythemis_uninstall` target in Makefile

[sashimanu-san]

Describe the bug
An uninstall makefile target is missing for python bindings.

To Reproduce
Steps to reproduce the behavior:

1. Use 'make pythemis_install'
2. Run 'make pythemis_uninstall'
3. See the following error:

make: *** No rule to make target 'pythemis_uninstall'.  Stop.

Expected behavior
Should be able to uninstall pythemis as it is the case with other language bindings (make phpthemis_uninstall and rbthemis_uninstall).

Environment (please complete the following information):

• OS: Debian 11.4
• Hardware: 64-bit
• Themis version: 0.14.0-23-g3a36aa4a
• Installation way:
  • via package manager
  • built from source

[vixentael]

yeah, makes sense, might add to

https://github.com/cossacklabs/themis/blob/master/Makefile#L606