Revert "stack.yaml: Update to lts-7.0 (ghc 8)"

This reverts commit e181603103.

This broke the i386ancient autobuilder due to its use of
--flag git-annex:XMPP --flag=git-annex:dbus

-- Failure when adding dependencies:
fdo-notify: needed ((>=0.3)), stack configuration has no specified version
(latest applicable is 0.3.1)
gnutls: needed ((>=0.1.4)), stack configuration has no specified version
(latest applicable is 0.2)
network-protocol-xmpp: needed (-any), stack configuration has no specified
version (latest applicable is 0.4.8)

OSX autobuilder also seems hosed by it, so too soon.

De-revert later..

CHANGELOG

@@ -12,7 +12,6 @@ git-annex (6.20160908) UNRELEASED; urgency=medium
   * copy, move, mirror: Support --json and --json-progress.
   * Improve gpg secret key list parser to deal with changes in gpg 2.1.15.
     Fixes key name display in webapp.
-  * stack.yaml: Update to lts-7.0 (ghc 8)
   * info: Support being passed a treeish, and show info about the annexed
     files in it similar to how a directory is handled.
   * sync: Previously, when run in a branch with a slash in its name,

stack.yaml

@@ -18,15 +18,8 @@ flags:
     androidsplice: false
 packages:
 - '.'
+resolver: lts-5.18
 extra-deps:
-- bloomfilter-2.0.1.0
-- esqueleto-2.4.3
-- network-multicast-0.1.1
-- persistent-2.2.4.1
-- persistent-sqlite-2.2.1
-- persistent-template-2.1.8.1
-- torrent-10000.0.0
-- yesod-default-1.2.0
+- process-1.3.0.0
 explicit-setup-deps:
   git-annex: true
-resolver: lts-7.0