[ARM GlobalISel] Remove redundant testcases. NFC

Remove the G_FADD testcases from arm-legalizer.mir, they are covered by
arm-legalizer-fp.mir (I probably forgot to delete them when I created
that test).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@316573 91177308-0d34-0410-b5e6-96231b3b80d8