tests: remove python_dependencies for smbserver from our tree

Users of the SMB tests will have to install impacket manually.

Reasoning: our in-tree version of impacket was quite outdated
and only compatible with Python 2 which is already end-of-life.
Upgrading to Python 3 and a compatible impacket version would
require to import additional Python-only and CPython-extension
dependencies. This would have hindered portability enormously.

Closes #5094

tests/data/test1451

@@ -28,6 +28,9 @@ Basic SMB request
 <command>
 -u 'curltest:curltest' smb://%HOSTIP:%SMBPORT/TESTS/1451
 </command>
+<precheck>
+python2 -c "__import__('pkgutil').find_loader('impacket') or (__import__('sys').stdout.write('Test only works if Python package impacket is installed\n'), __import__('sys').exit(1))"
+</precheck>
 </client>
 
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