[SYCL][NFC] Remove redundant __imf_fsigm* declarations

sycl/include/sycl/ext/intel/math.hpp

@@ -45,9 +45,6 @@ _iml_half_internal __imf_ceilf16(_iml_half_internal);
 float __imf_floorf(float);
 double __imf_floor(double);
 _iml_half_internal __imf_floorf16(_iml_half_internal);
-float __imf_fsigmf(float);
-_iml_half_internal __imf_fsigmf16(_iml_half_internal);
-_iml_bf16_internal __imf_fsigmbf16(_iml_bf16_internal);
 float __imf_rintf(float);
 double __imf_rint(double);
 _iml_half_internal __imf_invf16(_iml_half_internal);