RFR: 8295067: Remove virtual from ResourceObj::print_on

[Johan Sjölen]

We never use this method in any virtual manner. For example, we never iterate over `ResourceObj*` where the underlying types are different subclasses of `ResourceObj`. Removing `virtual` removes 8 bytes from each allocation (24 bytes -> 16 bytes) and also allows subclasses `print_on` to be non-`const`.

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Commit messages:
 - No longer virtual

Changes: https://git.openjdk.org/jdk/pull/10630/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10630&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295067
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/10630.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10630/head:pull/10630

PR: https://git.openjdk.org/jdk/pull/10630