ipcache/md: Make IPCache.metadata.remove() generic
ipcache/md: Make IPCache.metadata.remove() generic

Back in the commit "ipcache/md: Rework metadata cache for any labels",
the underlying mechanism for storing IP metadata was made more generic
to store any information that 'IPMetadata' represents. At the time, the
upsert codepaths were made generic to handle different types of incoming
information, but the remove paths remained specific to labels.

Now that the remove paths have been tidied up, we can more easily
abstract out the remove path as well. This should mean that future
patches which wish to store alternative types of information in the
ipcache should only need to update pkg/ipcache/types.go for the new data
type, then pull that information out in the main InjectLabels() loop in
order to create the new IPCache entry using the new info.

Signed-off-by: Joe Stringer <16a9a54ddf4259952e3c118c763138e83693d7fd@cilium.io>

cilium/cilium,cilium/cilium,cilium/cilium,cilium/cilium,cilium/cilium