Remove test which relied on now gone mongodb repository

Looks like Mongo doesn't provide any regular structure repository
anymore (only flat one?).

system/t04_mirror/CreateMirror28Test_gold

@@ -1,4 +0,0 @@
-Downloading http://downloads-distro.mongodb.org/repo/ubuntu-upstart/dists/dist/Release...
-
-Mirror [mirror28]: http://downloads-distro.mongodb.org/repo/ubuntu-upstart/ dist successfully added.
-You can run 'aptly mirror update mirror28' to download repository contents.

system/t04_mirror/CreateMirror28Test_mirror_show

@@ -1,19 +0,0 @@
-Name: mirror28
-Archive Root URL: http://downloads-distro.mongodb.org/repo/ubuntu-upstart/
-Distribution: dist
-Components: 10gen
-Architectures: amd64, i386
-Download Sources: no
-Download .udebs: no
-Last update: never
-
-Information from release file:
-Architectures: i386 amd64
-Codename: dist
-Components: 10gen
-Description:  mongodb packages
-
-Label: mongodb
-Origin: mongodb
-Suite: mongodb
-Version: dist

system/t04_mirror/create.py

@@ -354,21 +354,6 @@ class CreateMirror27Test(BaseTest):
         self.check_cmd_output("aptly mirror show mirror27", "mirror_show")
 
 
-class CreateMirror28Test(BaseTest):
-    """
-    create mirror: -force-components
-    """
-    runCmd = "aptly mirror create -ignore-signatures -force-components mirror28 http://downloads-distro.mongodb.org/repo/ubuntu-upstart dist 10gen"
-
-    def check(self):
-        def removeDates(s):
-            return re.sub(r"(Date|Valid-Until): [,0-9:+A-Za-z -]+\n", "", s)
-
-        self.check_output()
-        self.check_cmd_output("aptly mirror show mirror28",
-                              "mirror_show", match_prepare=removeDates)
-
-
 class CreateMirror29Test(BaseTest):
     """
     create mirror: repo with InRelease verification (internal GPG implementation)