[XLA:GPU] Cleanup: Use the new calling convention for non-fusion operations too and remove the old one

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[XLA:GPU] Cleanup: Use the new calling convention for non-fusion operations too and remove the old one

Reminder about the new calling convention:

• We pass all arguments / output buffers separately, not as a single temp_buff. Constant arguments are also passed as arguments to the kernel.
• This means that kernels don't have hardcoded offsets to their argument buffers, or references to the constant arguments, they simply receive direct pointers to them.
• If a kernel call has multiple parameters which are the same pointer, they are only passed once - to enable better optimizations.

This does not change kernel reuse:

• Fusion kernels are still reused.
• Non-fusion kernels are still not reused.

This CL shouldn't have a considerable runtime performance or compilation time effect. Tested it with internal benchmarks.

Test: Fixed HLO tests and added new calling_convention.hlo test.