Remove deprecated oneapi extensions

[KornevNikita]

Describe the bug

Currently we have 3 deprecated issues that have been deprecated in favor of core spec / khr extensions.
We need to:

1. deprecate the API (although I assume that it's deprecated already, but need to double-check and deprecate the leftover if any).
2. guard all deprecated stuff with #ifndef __INTEL_PREVIEW_BREAKING_CHANGES to remove in the next ABI-break window.
3. Need to move the specs to https://github.com/intel/llvm/tree/sycl/sycl/doc/extensions/removed and:
   3.1. Add "removed" section to each spec.
   3.2. Update the readme - add each spec to the table with a note why it has been removed.

Note - I suggest to remove each spec in a separate PR to avoid huge patches.

To reproduce

1. Include a code snippet that is as short as possible
2. Specify the command which should be used to compile the program
3. Specify the command which should be used to launch the program
4. Indicate what is wrong and what was expected

Environment

• OS: [e.g Windows/Linux]
• Target device and vendor: [e.g. Intel GPU]
• DPC++ version: [e.g. commit hash or output of clang++ --version]
• Dependencies version: [e.g. the output of sycl-ls --verbose]

Additional context

No response

[softwaresat]

Hi! I'm an ECE student at UT Austin and in Codepath's AI301 Open Source Capstone program and I would love to work on this issue. However, I have a 2–3 week development window. Since each deprecated issue is intended for a separate PR, which of the three would be the smallest and most suitable for a first-time contributor? I’d like to take ownership of that individual part first than the entire issue.