Revert "ArchiveUiTest now checks the snackbar when extracting archive"

This reverts commit 5c8c9b59.

Reason for revert: Checking the snackbar seems to make ArchiveUiTest
flaky (b/437254432). Sometimes, the tests don't detect the snackbar
even though it is visible in the screen recording.

Bug: 437254432
Flag: EXEMPT only test code
Test: atest DocumentsUIGoogleTests:com.android.documentsui.ArchiveUiTest
Change-Id: Ic66fee4f3c027bf5e45547971fe71c7144357073