Fix side effects of trace-ipc and dumpheap commands

These shell commands were implicitly deleting any client-named file for
which the system uid had deletion capability.  They no longer do this,
instead using only the client's own capabilities and file manipulation
modes.

Bug: 185398942
Test: manual "adb shell cmd activity dumpheap system_server /data/system/last-fstrim"
Test: atest CtsPermissionTestCases:ShellCommandPermissionTest
Change-Id: Ie61ab2c3f4bfbd04de09ca99c1116d1129461e8f