memref-test: Clean up ro_memref

We can't create memrefs to RO segments because these are not backed by
vmm_objs (b/149849862). This change removes related code and avoids
spamming logs with "ro memref create failed" messages.

Test: gem5 + trusty_tests memref.test
Bug: 149849862
Bug: 261816874
Change-Id: I8f14f7c28c921ea87a32b2faac28b8b9c8154d5a
2 files changed