Redundant dependencies in requirements.txt

[jonathanunderwood]

requirements.txt specifies unversioned dependencies on numpy and protobuf, both of which are (version constrained) dependencies of onnx, and so these are redundant and can be removed. For reference, the dependencies identified from poetry are:

├── onnxconverter-common >=1.7.0
│   ├── numpy *
│   ├── onnx *
│   │   ├── numpy >=1.16.6 (circular dependency aborted here)
│   │   ├── protobuf >=3.12.2
│   │   └── typing-extensions >=3.6.2.1
│   ├── packaging *
│   │   └── pyparsing >=2.0.2,<3.0.5 || >3.0.5
│   └── protobuf * (circular dependency aborted here)