gallium+glsl: Remove EmitNoSat/PIPE_CAP_VERTEX_SHADER_SATURATE

The drivers not setting it were:

- nv30, which gets lowering using NIR's lower_fsat flag.
- r300, which gets lowering using NIR's lower_fsat flag.
- a2xx, which has was getting it optimized back to fsat anyway.

This drops the check for the cap from gallium nine.  While nine does have
a non-nir path, I think it's safe to assume that if you have SM3
texturing, you can do fsat.

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16823>

src/compiler/glsl/ir_optimization.h

@@ -42,7 +42,6 @@ struct gl_shader_program;
 #define LDEXP_TO_ARITH     0x80
 #define CARRY_TO_ARITH     0x100
 #define BORROW_TO_ARITH    0x200
-#define SAT_TO_CLAMP       0x400
 #define DOPS_TO_DFRAC      0x800
 #define DFREXP_DLDEXP_TO_ARITH    0x1000
 #define BIT_COUNT_TO_MATH         0x02000