aco/dead_code_analysis: don't add artificial uses to p_startpgm

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20853>

src/amd/compiler/aco_dead_code_analysis.cpp

@@ -91,11 +91,6 @@ dead_code_analysis(Program* program)
       process_block(ctx, program->blocks[next_block]);
    }
 
-   /* add one use to exec to prevent startpgm from being removed */
-   aco_ptr<Instruction>& startpgm = program->blocks[0].instructions[0];
-   assert(startpgm->opcode == aco_opcode::p_startpgm);
-   ctx.uses[startpgm->definitions.back().tempId()]++;
-
    return ctx.uses;
 }