In many cases it was originally used to silence warnings about variables used
only in OSL_ENSURE etc., but that's no longer necessary since OSL_ENSURE is
based on SAL_WARN etc.  In some other cases it was apparently used as a
speculative debugging aid, to have a value assigned to a variable to be easily
able to view the value in a debugger.  And in some cases it was used with
(otherwise ignored) return values of (typically SQL-related) function calls, but
it is probably better to eventually find and fix all the problematic ones among
such calls via function declarations annotated SAL_WARN_UNUSED_RESULT.

Change-Id: Ib925b38da70073b546fdcd00fa8524dc302accbf