bignum_core: Removed input checking for `mbedtls_mpi_core_shift_l`

Signed-off-by: Minos Galanakis <minos.galanakis@arm.com>
diff --git a/library/bignum_core.h b/library/bignum_core.h
index 2b11cca..f719498 100644
--- a/library/bignum_core.h
+++ b/library/bignum_core.h
@@ -297,7 +297,7 @@
  * \brief               Shift an MPI in-place left by a number of bits.
  *
  *                      Shifting by more bits than there are bit positions
- *                      in \p X is valid and results in setting \p X to 0.
+ *                      in \p X will produce an unspecified result.
  *
  *                      This function's execution time depends on the value
  *                      of \p count (and of course \p limbs).