Hide the state of TinyPtrVector and remove the single element constructor.
Hide the state of TinyPtrVector and remove the single element constructor.

There is no reason for this state to be exposed as public. The single element
constructor was superfulous in light of the single element ArrayRef
constructor.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@226424 91177308-0d34-0410-b5e6-96231b3b80d8

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