Remove ureadahead package

The 'ureadahead' package was removed from Ubuntu at cosmic. The
last Debian release to distribute the 'readahead' was jessie. The
pkg-map already removes the package for redhat family of
distributions, so let's just remove it altogether.

Related-Bug: #1690891
Change-Id: I0e2df43384f327928f171665b3ce0bb5d60e3560

elements/amphora-agent/package-installs.yaml

@@ -61,7 +61,6 @@ screen:
 socat:
 tcpdump:
 ubuntu-cloudimage-keyring:
-ureadahead:
 uuid-runtime:
 vim-tiny:
 vlan:

elements/amphora-agent/pkg-map

@@ -21,11 +21,6 @@
         "screen": "",
         "dkms": ""
       }
-    },
-    "ubuntu": {
-      "focal": {
-        "ureadahead": ""
-      }
     }
   },
   "family": {
@@ -44,7 +39,6 @@
       "uuid-runtime": "",
       "ubuntu-cloudimage-keyring": "",
       "vim-tiny": "",
-      "ureadahead": "",
       "apt-transport-https": "",
       "pollinate": "",
       "ifupdown": "",