COMP: Update system to use CMake built-in macro "cmake_parse_arguments"

SLICER_PARSE_ARGUMENTS has been kept around but will display an error
message if it used by some extension. That will give the opportunity
for extension maintainer to update their CMakeLists.txt.

Considering that the file "CMakeParseArguments" is also included in the
code base associated with Slicer 4.2.2-1, simply updating the extension
so that "cmake_parse_arguments" is used will be sufficient. Say differently,
CMakeLists.txt maintained for both extension build against Slicer nightly
and Slicer 4.2.2-1 won't diverge.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21774 3bd1e089-480b-0410-8dfb-8563597acbee
COMP: Fix warning "Slicer_BUILD_SkullStripper" is unused.

The option has been added by r18797, then when SkullStripper
has been converted to be a regular extension (r20088) the variable
"Slicer_BUILD_SkullStripper" should have been removed from SuperBuild.cmake.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21775 3bd1e089-480b-0410-8dfb-8563597acbee