Remove libunwind from VNDK

libunwind in VNDK is no longer used by vendor modules. So we may
remove it from VNDK.
However, there are still some vendor modules that are using static
variant of libunwind. For those vendor modules, we define
libunwind_static and make it available to vendor.

Bug: 120948701
Test: build and boot
Change-Id: I2678d94a60703a35d3bc6aad8b20a86f72e67913