Remove BUILD_CONST_KEY_MAP opcode #122160

According to our stats the BUILD_CONST_KEY_MAP represents fewer than 1 in 20_000 instructions executed.

Presumably it is more common in startup code, but it has no real value there either.
For run once code, turning the keys into a constant merely moves the cost of building the keys from the interpreter to unmarshalling.

Linked PRs

• GH-122160: Remove BUILD_CONST_KEY_MAP opcode. #122164