fix Issue 10684 - Refused array op with array literal

Accept array literals as the operand of array-ops.

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Since, array-ops had required explicit slice to the array literal operands,
eg. `a[] = [1,2][] + c[];`

By the commit:
https://github.com/9rnsr/dmd/commit/f703c5c6551affddd9213f759657a2b3e391b935
now the redundant slice operators at the right side of an array literal is
entirely removed - `[1,2,3][][]` is rewritten to `[1,2,3]`.

Although it has broke existing code using array-ops, I still cannot think
the optimization was incorrect.

On the other hand, I could not find the description about the necessity of
explicit slice on array literal from the language spec.
http://dlang.org/arrays.html#array-operations
It looked to me that is just an implementation-specific restriction.

So, I implemented this as the easiest way to fix the issue.