sqlite3: always build a thread-safe library

sqlite3: always build a thread-safe library

Pull request #9033 showed that there are problems with builds where
thread-safe mode is disabled. The binaries still reference functions
from libpthread. This commit removes the thread-safe choice for now.
Once this is addressed upstream the choice can be added back.

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>