[RISCV] Remove the TODO for lowering f32 libcall on RV64 with lp64 abi. (NFC)

The unnecessary extension doesn't exist anymore after https://reviews.llvm.org/D65497.

Author: tclin914

llvm/test/CodeGen/RISCV/rv32i-rv64i-float-double.ll

@@ -9,8 +9,6 @@
 ; legalisation or DAG combines aren't incorrectly triggered when the F
 ; extension isn't enabled.
 
-; TODO: f32 parameters on RV64 with a soft-float ABI are anyext.
-
 define float @float_test(float %a, float %b) nounwind {
 ; RV32IF-LABEL: float_test:
 ; RV32IF:       # %bb.0: