configure.ac: remove a non-valid character

This patch removes a non-valid character inside HAVE_COREAUDIO.
This char is difficult to see if you editor is not able
to show non-valid char.

But carefully checking configure log show this text without the patch:

./configure: line 6831: $'\302\240test': command not found

You can also see it using Emacs that detects such bad char.

Change-Id: I1e1e62fb6e03c42ac9d9758bc44db33fad088482
Tuleap: #909