remove async build dep

Not needed.. At least for now..

debian/control

@@ -42,7 +42,6 @@ Build-Depends:
 	libghc-network-protocol-xmpp-dev (>= 0.4.3-1+b1),
 	libghc-gnutls-dev (>= 0.1.4),
 	libghc-xml-types-dev,
-	libghc-async-dev,
 	ikiwiki,
 	perlmagick,
 	git,

doc/install/fromscratch.mdwn

@@ -19,7 +19,6 @@ quite a lot.
   * [edit-distance](http://hackage.haskell.org/package/edit-distance)
   * [hS3](http://hackage.haskell.org/package/hS3) (optional)
   * [SafeSemaphore](http://hackage.haskell.org/package/SafeSemaphore)
-  * [async](http://hackage.haskell.org/package/async)
 * Optional haskell stuff, used by the [[assistant]] and its webapp (edit Makefile to disable)
   * [stm](http://hackage.haskell.org/package/stm)
     (version 2.3 or newer)

git-annex.cabal

@@ -57,7 +57,7 @@ Executable git-annex
    pcre-light, extensible-exceptions, dataenc, SHA, process, json, HTTP,
    base (>= 4.5 && < 4.7), monad-control, transformers-base, lifted-base,
    IfElse, text, QuickCheck >= 2.1, bloomfilter, edit-distance, process,
-   SafeSemaphore, async
+   SafeSemaphore
   -- Need to list these because they're generated from .hsc files.
   Other-Modules: Utility.Touch Utility.Mounts
   Include-Dirs: Utility