MdeModulePkg/FileExplorer: Remove the codes of searching load file protocol

MdeModulePkg/FileExplorer: Remove the codes of searching load file protocol

https://bugzilla.tianocore.org/show_bug.cgi?id=323

FileExplorer no need to search load file protocol to show files.
Now remove the codes.

Cc: Eric Dong <eric.dong@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>