sh: Use DQSYNTAX only while expanding, not SQSYNTAX.

Quoting during expansion only cares about CCTL, which is the same for
DQSYNTAX and SQSYNTAX.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274854 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f