Revert "ANDROID: Incremental fs: Use R/W locks to read/write segment blockmap."

This reverts commit 53f6b6a6.

Set incfs back to rvc shipping incfs

Bug: 178509184
Test: incfs_test passes
Signed-off-by: Paul Lawrence <paullawrence@google.com>
Change-Id: I7c77704f722f9949b8a7b7a40829c29abab1357e