COMP: Fix warning removing explicit setting of CMake policy CMP0017.

Setting of CMP0017 to OLD is not needed.

This commit addresses the following warning reported when using CMake 3.9.0:

```
CMake Deprecation Warning at /path/to/Slicer-build/BRAINSTools/CMakeLists.txt:11 (cmake_policy):
  The OLD behavior for policy CMP0017 will be removed from a future version
  of CMake.

  The cmake-policies(7) manual explains that the OLD behaviors of all
  policies are deprecated and that a policy should be set to OLD only under
  specific short-term circumstances.  Projects should be ported to the NEW
  behavior and not rely on setting a policy to OLD.
```

See Slicer/Slicer#765

CMakeLists.txt

@@ -7,9 +7,6 @@ endif()
 if(POLICY CMP0048)
  cmake_policy(SET CMP0048 OLD) #OLD project() behavior for setting VERSION variable
 endif()
-if(POLICY CMP0017)
- cmake_policy(SET CMP0017 OLD) #Prefer files from the CMake module directory when including from there
-endif()
 foreach(p
  CMP0054 # CMake 3.1 Only interpret ``if()`` arguments as variables or keywords when unquoted.
 # CMP0042 # ``MACOSX_RPATH`` is enabled by default.