Remove fixme comment about clobber_abi on PowerPC

Author: taiki-e

compiler/rustc_target/src/asm/mod.rs

@@ -1138,8 +1138,6 @@ impl InlineAsmClobberAbi {
                     f8, f9, f10, f11, f12, f13,
 
                     // v0-v19
-                    // FIXME: PPC32 SysV ABI does not mention vector registers processing.
-                    // https://refspecs.linuxfoundation.org/elf/elfspec_ppc.pdf
                     v0, v1, v2, v3, v4, v5, v6, v7,
                     v8, v9, v10, v11, v12, v13, v14,
                     v15, v16, v17, v18, v19,