PKGBUILD suggestions

• Remove python packages from makedepends
  • Bazel hermetic python build only uses python itself. python-installer is needed to install the generated wheel in $pkgdir.
  • Implements #15 (closed).
• Remove dependencies on python-keras-applications python-keras-preprocessing
  • Both packages were moved into python-keras and tensorflow.
  • https://github.com/keras-team/keras-applications/commit/06fbeb0f16e1304f239b2296578d1c50b15a983a
  • https://github.com/keras-team/keras-preprocessing/commit/3e380065d4afc7347aaee8d89325a16b22158438
  • Related python-keras!1.