debug/gdb: cleanup (remove) the static ncurses build

ncurses is built solely for the sake of building a native gdb.
The user should not rely on this library to build his/her userland,
but should rather build his/her own. So we remove it from the
sysroot after we successfully build the native gdb.

 reporter_name="YEM"

 reporter_url="http://ymorin.is-a-geek.org/"

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