ShellPkg/Shell: Use BaseLib api CharToUpper

ShellPkg/Shell: Use BaseLib api CharToUpper

Substitute InternalShellCharToUpper with a public function
CharToUpper which has the same function.
Remove the implement of InternalShellCharToUpper.

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Jaben Carsey <jaben.carsey@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Shenglei Zhang <shenglei.zhang@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>