Remove magic '-DBUILDING_CBSASL' and '-DCBSASL_STATIC' flags

We're embedding this and shouldn't make this visible. Also, upstream has
removed the 'static' functionality, and it would be nice if we didn't
actually export the symbols

Change-Id: If04f12356936f111fedbd88883011253208b22dc
Reviewed-on: http://review.couchbase.org/43796
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>