meminfo: Remove libpagemap dependency

Remove all tests that validated libmeminfo against the libpagemap
implementation and make libmeminfo_test self sufficient.

Bug: 111694435
Bug: 113035067
Test: libmeminfo_test
Change-Id: I21b9a0e2c71ef3f1f672a3b1de8080c0c36b4bfe
Signed-off-by: Sandeep Patil <sspatil@google.com>