apt: upgrade to 0.7.3

* 0.7.2 has become unfetchable on the Debian mirrors
* 0.7.2 was broken (failed do_patch), the same applies for 0.7.3.
  IOW, it was broken before, it is still broken now, but
  hopefully less so.
* more information in bug 2017 comment 6

diff --git a/packages/apt/apt-0.7.2/.mtn2git_empty b/packages/apt/apt-0.7.3/.mtn2git_empty
similarity index 100%
rename from packages/apt/apt-0.7.2/.mtn2git_empty
rename to packages/apt/apt-0.7.3/.mtn2git_empty

diff --git a/packages/apt/apt_0.7.2.bb b/packages/apt/apt_0.7.3.bb
similarity index 100%
rename from packages/apt/apt_0.7.2.bb
rename to packages/apt/apt_0.7.3.bb