cython: drop egg-info; fix python shebang

- Drop egg-info, not needed
- Use python via `/usr/bin/env`, otherwise it hardcodes not-relocated
  full path to Python. This generates unwanted RPM dependencies, e.g.,
```
  rpm -qp --requires external+cython+0.19.1-1-1.fc19_aarch64_gcc490.rpm
  [snip]
  /home/david.abdurachmanov/real-arch/allext/a/fc19_aarch64_gcc490/external/python/2.7.6/bin/python
  [snip]
```

```
[davidlt@lxplus0191]/afs/cern.ch/cms/slc6_amd64_gcc481/external/cython/0.19.1-cms% grep -n -R 'bin/python' *
bin/cygdb:1:#!/build/degano/CMSSW_7_2_0_pre1-build/slc6_amd64_gcc481/external/python/2.7.6/bin/python
bin/cython:1:#!/build/degano/CMSSW_7_2_0_pre1-build/slc6_amd64_gcc481/external/python/2.7.6/bin/python
lib/python2.7/site-packages/Cython/Debugger/libpython.py:1:#!/usr/bin/python
```


Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>