Remove "Preview" from CMake feature name and related places

[jonahgraham]

With one of the goals of CDT 12 being making CMake a first class citizen of CDT, I think we need to remove the Preview in the feature name:

cdt/cmake/org.eclipse.cdt.cmake-feature/feature.properties

Line 18 in af1b6fa

featureName=C/C++ CMake Build Support - Preview

This is what it looks like to users who are installing it: