Since now we can distinguish between def and use according to
the variable's location, there is no need to keep two variable
prefixes.
Also reformat tests to use the value generating instruction
format ("<result-id> = <opcode> <operand>..").
For enum Capability and enum Op, not all newly added enumerants are
registered into capabilityInfoEntries and opcodeTableEntries yet.
That will come in following commits.
