remove nix section to unbreak i386-ancient build

doc/bugs/Add_day_to_metadata./comment_2_ea15c799c5abfc97eaa20424c15b73a4._comment

@@ -0,0 +1,12 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 2"""
+ date="2017-11-08T18:51:20Z"
+ content="""
+Unfortunately the added nix section broke the i386-ancient build,
+which uses stack 1.0.4. That version of stack complains:
+
+Executable named nix-shell not found on path: ["/usr/local/sbin","/usr/local/bin","/sbin","/bin","/usr/sbin","/usr/bin"]
+
+So, I've reverted the addition of that section.
+"""]]

stack.yaml

@@ -24,11 +24,3 @@ extra-deps:
 explicit-setup-deps:
   git-annex: true
 resolver: lts-9.9
-nix:
-  packages:
-    - ncurses
-    - icu
-    - libcxx
-    - gcc
-    - zlib
-    - rsync