MdeModulePkg/Bds: Remove assertion in BmCharToUint

BmCharToUint() could be called using external data and it
already contains logic to return -1 when data is invalid,
so removing unnecessary assertion to avoid system hang.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

MdeModulePkg/Library/UefiBootManagerLib/BmMisc.c

@@ -420,7 +420,6 @@ BmCharToUint (
     return (Char - L'A' + 0xA);
   }
 
-  ASSERT (FALSE);
   return (UINTN) -1;
 }