glsl: Move exp/log-to-exp2/log2 lowering to glsl-to-NIR.

It's way more concise to write as nir_builder calls.

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

@@ -36,8 +36,6 @@ struct gl_shader_program;
 /* Operations for lower_instructions() */
 #define SUB_TO_ADD_NEG     0x01
 #define FDIV_TO_MUL_RCP    0x02
-#define EXP_TO_EXP2        0x04
-#define LOG_TO_LOG2        0x10
 #define INT_DIV_TO_MUL_RCP 0x40
 #define LDEXP_TO_ARITH     0x80
 #define CARRY_TO_ARITH     0x100