Delete `gtNewBlkOpNode` and `lvSimdBaseJitType` (#85848)

Delete `gtNewBlkOpNode` and `lvSimdBaseJitType` (#85848)

* Delete "gtNewBlkOpNode"

Note: neither "initobj" nor "cpobj" can be preceded by "volatile.".

Delete the self-assignment handling

Block morphing will fold it to a NOP anyway.

I do not see the referenced liveness bug still being present.
It seems to have been a remnant of COPYBLK/COPYOBJ days.

Move the SIMD logic to gtNewAssignNode

Delete "gtNewBlkOpNode"

* Delete lvSimdBaseJitType