shader_recompiler: Remove S32 IR type

The frontend IR opcodes do not distinguish between signed and unsigned integer types.

Fixes broken shaders when IR validation/graphics debugging is enabled for shaders that used BitCastS32F32

src/shader_recompiler/backend/spirv/emit_spirv_bitwise_conversion.cpp

@@ -18,10 +18,6 @@ void EmitBitCastU64F64(EmitContext&) {
     throw NotImplementedException("SPIR-V Instruction");
 }
 
-void EmitBitCastS32F32(EmitContext&) {
-    throw NotImplementedException("SPIR-V Instruction");
-}
-
 void EmitBitCastF16U16(EmitContext&) {
     throw NotImplementedException("SPIR-V Instruction");
 }