missing (opt)depends and improvement

Description:

1. Per to upstream requirements.txt,'python-yara' 'python-capstone' 'python-pycryptodome' should be optdepends instead of depends.
2. Per to upstream requirements.txt, 'python-leechcorepyc' should be added to optdepends, which is not in [extra] currently.
3. Per to upstream requirements-dev.txt, 'python-jsonschema' is only recommended for development, thus should be removed.
4. 'python-snappy' is not used and should be removed. volatility3/framework/layers/avml.py searches for "libsnappy.so.1" directly. So 'snappy' should be added as optdepends.

Additional info:

• package version(s): 2.5.0-1