ShellPkg/Dp: Make the help info align with code

ShellPkg/Dp: Make the help info align with code

Currently in DP, the Trace mode is enabled by default.
And the profile mode is not implemented. but the help info
of DP tool doesn't match current implementation. Which will
make user confused. So now remove the unused source code
related to the profile mode and update the help information
of DP tool.

V2: Remove the unused code related to profile mode.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Jaben Carsey <jaben.carsey@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>