Fix a misleading warning message about sysprop overriding

Regardless of whether a system property is "ro." or not, it can be
overridden by build.prop from the more specific partition. i.e.
foo.bar=true in system/build.prop can be overridden by
foo.bar=false in vendor/build.prop. However, the warning message
was referring the overridden property as "ro." causing confusion
when reading the log. Fix it by not mentioning "ro.".

Bug: 117892318
Test: N/A
Change-Id: I13014522d0c6b507b30c8754e2087fd71cc39971