Merge PEI & DXE LzmaCustomDecompressLib. A previous implementation

Merge PEI & DXE LzmaCustomDecompressLib.  A previous implementation
was causing the LZMA decompression code to request a large buffer,
which caused an ASSERT to fail for PEI's AllocatePool.  The
current implementation, which uses the LzmaDecode function, does
not have this issue and therefore both the PEI & DXE versions can
use AllocatePool/FreePool.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@8236 6f19259b-4bc3-4df7-8a09-765794883524