[SPIRV] Avoid OpQuantizeToF16 in SPIR-V kernel test (#158086)
This PR resolves the current failure in the `integer-casts.ll` SPIR-V
test during CI runs in `llvm-project`.
The failure occurs because the SPIR-V instruction `OpQuantizeToF16`
requires the `Capability::Shader`. However, the function in
`integer-casts.ll` is written as a kernel function and executed in a
kernel environment. Therefore, `Capability::Kernel` is emitted instead
of `Capability::Shader`. To fix this, we remove the `QuantizeToF16` test
from`integer-casts.ll` in this PR.