MdeModulePkg EhciPei: Remove a redundant function

MdeModulePkg EhciPei: Remove a redundant function

The function UsbHcUnlinkMemBlock that is never called
and its related comments have been removed.
It is missed in the patch series according to the log in
https://bugzilla.tianocore.org/show_bug.cgi?id=1062

v2:Update the title.

Cc: Star Zeng <star.zeng@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: shenglei <shenglei.zhang@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>