Remove unused Windows sources

Remove unused Windows sources

windows/build and windows/installer/nsis are not used by the KfW 4.x
build process.  windows/wintel was removed from the build in commit
530043377ee6f39b9ca95c13f6260602e6fe7674.  windows/cns and most of the
windows/lib objects were removed from the build in commit
52fa910f413e016b3d432ce34e2d5bcea3230a7d.  Most of the Leash krb4
files were removed from the build in commit
9f097418620513813ecc086bcd9002b6e07bf2a1; some unnecessary includes of
the corresponding header files remain, so delete those now.
LeashControlPanel.cpp was not part of the leash build when the leash
sources were imported into this tree.