MdePkg/BaseLib: Move CHAR_NULL definition to Base.h in BaseLib

- Required unicode control chars -> Null character
- Remove CHAR_NULL definition in SimpleTextIn.h
- https://bugzilla.tianocore.org/show_bug.cgi?id=172

Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Bell Song <binx.song@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

MdePkg/Library/BaseLib/FilePaths.c

@@ -10,10 +10,8 @@
   THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
   WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
 **/
-#include  <Uefi/UefiBaseType.h>
 #include  <Library/BaseMemoryLib.h>
 #include  <Library/BaseLib.h>
-#include  <Protocol/SimpleTextIn.h>
 
 /**
   Removes the last directory or file entry in a path by changing the last