Remove special handling for missing crypto_blkdev

Remove special handling for missing crypto_blkdev

This logic is no longer necessary, since the code that creates the
crypto_blkdev (create_crypto_blk_dev() in MetadataCrypt.cpp or in
cryptfs.cpp) now waits for the block device to appear before continuing.

It's also worth noting that the retry loop was only present for ext4,
not for f2fs, yet most Android devices are using f2fs these days.

Test: see I08fc8465f7962abd698904b5466f3ed080d53953
Change-Id: I173ca6cc187a810e008990dfa22aede58632db25