[FastISel] Remove an performance debugging assert.
[FastISel] Remove an performance debugging assert.

As Jim pointed out this assert isn't really needed to test for correctness,
because the code right afterwards does the same check and falls-back to
SelectionDAG - as intended.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@215735 91177308-0d34-0410-b5e6-96231b3b80d8

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