Revert "Revert "Remove a misleading "flush" function.""

This reverts commit 47da1774.

Reason for revert: Fixed the test broken by the original commit

Bug: 139192244
Bug: 140336855

Test: m -> flash -> boot
Test: atest CtsJvmtiAttachingHostTestCases

Change-Id: I4c67ad8709652c4710ef24564e0240f74f817f8c