Revert "configure: link flite against libasound"

This reverts commit 396648cc.

The commit made impossible to build against libflite if libasound is not
available (e.g. on Windows). Thus remove the -lasound flag. In case of
libflite static linking the workaround is to enable
--extra-ldflags=-lasound (or disable the ALSA output device in libflite).