Refactor some codes for unbundle (4/N)

* Use FormatUtils.formatDuration to instead of
  DateUtils.formatDuration
* Use openProxyFileDescriptor(int, ProxyFileDescriptorCallback,
  Handler) to instead of openProxyFileDescriptor(int,
  ProxyFileDescriptorCallback) of StorageManager
* Remove redundant code

Bug: 118794189
Fix: 120622853
Test: atest DocumentsUITests
Change-Id: Id86d4aaa58225e1afdc0debdd6837eaec72e7d95