no importKey for android yet

adb shell has sha256sum sha1sum and some others, so they could be used.
They're provided by toybox, so seem about as likely to keep
working as find and stat, which it already depends on.

Or to not add a dep, could use stat the same as getExportContentIdentifier
to get a mtime, and make a WORM key. But do I really want this to
default to WORM?

Unsure what's the best path, so punting for now.

CHANGELOG

@@ -1,8 +1,8 @@
 git-annex (8.20200618) UNRELEASED; urgency=medium
 
   * import: Added --no-content option, which avoids downloading files
-    from a special remote. Only supported by some special remotes:
-    directory
+    from a special remote. Currently only supported by the directory
+    special remote.
   * Honor annex.largefiles when importing a tree from a special remote.
     (Except for when --no-content is used.)
   * Fix a deadlock that could occur after git-annex got an unlocked

Remote/Adb.hs

@@ -81,6 +81,7 @@ gen r u rc gc rs = do
 			}
 		, importActions = ImportActions
 			{ listImportableContents = listImportableContentsM serial adir
+			, importKey = Nothing
 			, retrieveExportWithContentIdentifier = retrieveExportWithContentIdentifierM serial adir
 			, storeExportWithContentIdentifier = storeExportWithContentIdentifierM serial adir
 			, removeExportWithContentIdentifier = removeExportWithContentIdentifierM serial adir