include locally deleted by remotely present branches in bash-completion for git push --delete

[Karl-Philipp Richter]

In case the `--delete` of `git push` option is used it makes sense to offer branches which don't exist locally, but remotely as well.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: bash-completion 1:2.1-4ubuntu1
Uname: Linux 4.0.1-040001-generic x86_64
ApportVersion: 2.17.2-0ubuntu1
Architecture: amd64
CurrentDesktop: Unity
Date: Wed May 20 14:49:36 2015
EcryptfsInUse: Yes
InstallationDate: Installed on 2015-04-02 (47 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Beta amd64 (20150326)
PackageArchitecture: all
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: bash-completion
SystemImageInfo:
 current build number: 0
 device name:
 channel: daily
 last update: Unknown
UpgradeStatus: No upgrade log present (probably fresh install)