[clang][NFC] Fix and simplify the test added in 8dcc7eecb75b39d723fd6fee566369bf67e43fdf
We only have to create a TypeTraitExpr node with 16 bits worth of
arguments to detect an overflow with the assertion added in the
constructor of TypeTraitExpr. Moreover the static_assert in
original test is pointless since __is_constructible only check
that the corresponding expression is well-formed.