Remove unused mocket from test dependencies

[frenzymadness]

If I understand it correctly, all tests are passing without mocket for me and I don't see its usage anywhere in the codebase. So I believe it should be removed from test dependencies.

[frenzymadness]

Output without mocket:

============================= test session starts ==============================
platform linux -- Python 3.10.0rc2, pytest-6.2.5, py-1.10.0, pluggy-1.0.0
rootdir: /builddir/build/BUILD/maxminddb-2.2.0
collected 255 items

tests/decoder_test.py ..............                                     [  5%]
tests/reader_test.py ................................................... [ 25%]
........................................................................ [ 53%]
........................................................................ [ 81%]
..............................................                           [100%]

============================= 255 passed in 1.75s ==============================

[oschwald]

Thanks!