[NFC][ARM][ParallelDSP] Refactor narrow sequence
[NFC][ARM][ParallelDSP] Refactor narrow sequence

Most of the code used for finding a 'narrow' sequence is not used,
so I've removed it and simplified the calls from the smlad matcher.


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@362104 91177308-0d34-0410-b5e6-96231b3b80d8

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