Howard Chu authored Sep 09, 2020 and Quanah Gibson-Mount committed Sep 09, 2020

Using cs_pmutex. Reverts the addition of cs_modmutex in ITS#9330,
use cs_pmutex for both delta and plain writes.

Note that plain syncrepl already used cs_pmutex when a cookie CSN
was present in the op. Now it is used for all writes, regardless
of presence of cookie.