Remove a final dependency on the form field in tablegen; which is a remnant
of the old jit and which we don't intend to support in mips16 or micromips.
This dependency is for the testing of whether an instruction is a pseudo.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175297 91177308-0d34-0410-b5e6-96231b3b80d8