brw: Remove extra SHADER_OPCODE_FLOW emitted during NIR conversion

The DO() helper already emits a FLOW.

Fixes: d2c39b1779 ("intel/brw: Always have a (non-DO) block after a DO in the CFG")
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33954>

src/intel/compiler/brw_from_nir.cpp

@@ -471,8 +471,6 @@ brw_from_nir_emit_loop(nir_to_brw_state &ntb, nir_loop *loop)
    assert(!nir_loop_has_continue_construct(loop));
    bld.DO();
 
-   bld.emit(SHADER_OPCODE_FLOW);
-
    brw_from_nir_emit_cf_list(ntb, &loop->body);
 
    brw_inst *peep_while = bld.emit(BRW_OPCODE_WHILE);