MANAGE_EXTERNAL_STORAGE cleanup: remove isIgnoredAppOp

We previously had to add this to fix an issue where we used to setMode
instead of setUidMode. Now that this change has rolled out to DP2 and
the relevant populations, we can safely remove this check.

Test: build
Fix: 149995538
Change-Id: Ib6ba0a9bdacb16cc53f5883d34d67c2df92d4161