Remove mock_configs; tests no longer modify spack home directory.

var/spack/mock_configs/site_spackconfig/compilers.yaml

@@ -1,12 +0,0 @@
-compilers:
-  all:
-    clang@3.3:
-      cc: /path/to/clang
-      cxx: /path/to/clang++
-      f77: None
-      fc: None
-    gcc@4.5.0:
-      cc: /path/to/gcc
-      cxx: /path/to/g++
-      f77: /path/to/gfortran
-      fc: /path/to/gfortran