WinRT: removed '-' from build script file names

Most of the other build scripts don't include a '-' in their file names.  This
change makes the WinRT build scripts use the same convention.

--HG--
rename : build-scripts/winrt-build.bat => build-scripts/winrtbuild.bat
rename : build-scripts/winrt-build.ps1 => build-scripts/winrtbuild.ps1