Stop generation of integration header in runtime compilation mode

### Is your feature request related to a problem? Please describe

The extension to compile SYCL code at runtime (#11985) only allows to compile SYCL device code at runtime, it does not specify an API to compile additional host code at runtime. Therefore, there is no need to generate the integration header during runtime compilation of SYCL code.

#15892, as a first step, removes some restrictions on free-function kernels that are needed for correct integration header support by omitting some tests and parts of the integration header.

As discussed in the PR, a next step would be to entirely stop emitting the integration header when compiling SYCL code at runtime.

### Describe the solution you would like

No integration header generated when compiling SYCL code at runtime in runtime compilation mode.

### Describe alternatives you have considered

_No response_

### Additional context

_No response_