RFR: 8297766: Remove UseMallocOnly development option

[Afshin Zafari]

### Description
The UseMallocOnly development option was originally used to detect memory stomping bugs with Arena allocations when the JVM was first in development.

The option has had a few bugs and is not in general use. There are ideas to add another way of Arena canary checking.

### Patch:
All occurrences of UseMallocOnly are removed.

### Tests:
Local, gTests: resourceArea and Arena
Mach5: tier1-5

-------------

Commit messages:
 - 8297766: Remove UseMallocOnly development option
 - 8297766: Remove UseMallocOnly development option
 - UseMallocOnly instances are removed

Changes: https://git.openjdk.org/jdk/pull/11456/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11456&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297766
  Stats: 219 lines in 8 files changed: 1 ins; 196 del; 22 mod
  Patch: https://git.openjdk.org/jdk/pull/11456.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11456/head:pull/11456

PR: https://git.openjdk.org/jdk/pull/11456