package/libsolv: drop unrecognized variables

Drop unrecognized variables:

CMake Warning:
  Manually-specified variables were not used by the project:

    BUILD_DOC
    BUILD_DOCS
    BUILD_EXAMPLE
    BUILD_EXAMPLES
    BUILD_TEST
    BUILD_TESTING
    BUILD_TESTS
    CMAKE_CXX_COMPILER_FORCED
    DISABLE_STATIC
    ENABLE_SHARED

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>