It seems as recent versions of `trezor` don't work with python 2.x:
```
/build/trezor-0.9.1/dist /build/trezor-0.9.1
Processing ./trezor-0.9.1-py2-none-any.whl
trezor requires Python '>=3.3' but the running Python is 2.7.15
builder for '/nix/store/aqyxki0ckanjk4r1f0an4kj1w4s3kk4f-python2.7-trezor-0.9.1.drv' failed with exit code 1
cannot build derivation '/nix/store/gp4smkzc9r87lzajs17jnq4rh2ayc5q0-python2.7-keepkey-4.0.0.drv': 1 dependencies couldn't be built
```
The `buildPython*` function computes name from `pname` and `version`.
This change removes `name` attribute from all expressions in
`pkgs/development/python-modules`.
While at it, some other minor changes were made as well, such as
replacing `fetchurl` calls with `fetchPypi`.
Regression introduced by 76beb08313.
With version 0.7.15 a few additional dependencies are needed by trezor,
mainly a newer version of protobuf bindings and requests.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
Cc: @np
