Revert "[platform process list] add a flag for showing the processes of all users"

Summary:
This reverts commit e4ac611cd787f3f0e727a394e96fb1a5c3b19ccb.

There's a failure according to http://lab.llvm.org:8080/green/view/LLDB/job/lldb-cmake/2538/testReport/junit/lldb-api/functionalities_gdb_remote_client/TestPlatformClient_py/

Reviewers: labath, aadsm, clayborg

Subscribers: lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D68883

llvm-svn: 374603