Fix confusing javadoc for WifiManager.EXTRA_RESULTS_UPDATED

This rephrases the javadoc for WifiManager.EXTRA_RESULTS_UPDATE
and WifiManager.SCAN_RESULTS_AVAILABLE_ACTION, explaining the
meaning of WifiManager.EXTRA_RESULTS_UPDATED in a better way.
This also removes "supplicant" keyword in this javadoc because
we no longer use supplicant for scan.

Bug: 62273016
Test: compile
Change-Id: Ib8ce2d6e8aaf70819c9e2622fb5acfcc14a0d593