intel/brw: Don't force g1's live range to be the entire program

The idea here was that pixel shader framebuffer writes used the g0 and
g1 thread payload register values to construct the message header.
However, most messages are headerless and don't use either.  There's a
2012-era comment that the simulator at one point had a bug where certain
headerless messages would incorrectly take the values from the g0/g1
register contents rather than using sideband.  But, that was likely
fixed eons ago.  So we really don't need to do this.

Furthermore, there are many more shader stages these days:
- VS: r1 contains output URB handles
- TCS: r1 contains ICP handles
- TES: r1 contains gl_TessCoord.x (r4 contains output URB handles)
- GS: r1 contains output URB handles
- CS: r1 contains LocalID.X on DG2+ but nothing on older hardware
- Task/Mesh: r1 contains LocalID.X
- BS: r1 contains bindless stack handles

Vertex and geometry aren't likely to benefit here because r1 is needed
for their output messages, which are also what terminate the shader.
TES will definitely benefit because we were making a value pointlessly
live for the whole program.  Same for TCS, to a lesser extent.  Compute
prior to DG2 was the worst, as g1 literally has no meaningful content,
so there is no point to keeping it live.

fossil-db on Alchemist shows substantial spill/fill improvements:

   Totals:
   Instrs: 148782351 -> 148741996 (-0.03%); split: -0.03%, +0.01%
   Cycles: 12602907531 -> 12605795191 (+0.02%); split: -0.70%, +0.72%
   Subgroup size: 7518608 -> 7518632 (+0.00%)
   Send messages: 7341727 -> 7341762 (+0.00%)
   Spill count: 54633 -> 52575 (-3.77%)
   Fill count: 104694 -> 100680 (-3.83%)
   Scratch Memory Size: 3375104 -> 3287040 (-2.61%)

   Totals from 301172 (48.21% of 624670) affected shaders:
   Instrs: 95531927 -> 95491572 (-0.04%); split: -0.05%, +0.01%
   Cycles: 9643531593 -> 9646419253 (+0.03%); split: -0.91%, +0.94%
   Subgroup size: 4492512 -> 4492536 (+0.00%)
   Send messages: 4399737 -> 4399772 (+0.00%)
   Spill count: 20034 -> 17976 (-10.27%)
   Fill count: 41530 -> 37516 (-9.67%)
   Scratch Memory Size: 1522688 -> 1434624 (-5.78%)

Assassin's Creed Odyssey in particular has 20% fewer fills.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30146>

src/intel/compiler/brw_fs_reg_allocate.cpp

@@ -229,7 +229,6 @@ void fs_visitor::calculate_payload_ranges(unsigned payload_node_count,
           * reserve it.
           */
          payload_last_use_ip[0] = use_ip;
-         payload_last_use_ip[1] = use_ip;
       }
 
       ip++;