RFR: 8271946: Cleanup leftovers in Space and subclasses [v2]

[Roman Kennke]

> There are a number of methods in (Compactible)Space that seem trivially implemented. E.g. obj_size(), adjust_obj_size(), scanned_block_is_obj() etc. I believe they are leftovers from CMS (not sure) but looks like they can be replaced by obj->size() or removed altogether. Also, the the related templated methods scan_and_forward(), scan_and_adjust_pointers() and scan_and_compact() can be directly and mechanically inlined into their callers. It makes the code more readable.
> 
> Testing:
>  - [x] hotspot_gc
>  - [x] tier1
>  - [ ] tier2

Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:

  Remove obsolete comments

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5031/files
  - new: https://git.openjdk.java.net/jdk/pull/5031/files/41fe28ea..ebaa84b8

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5031&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5031&range=00-01

  Stats: 15 lines in 1 file changed: 0 ins; 15 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5031.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5031/head:pull/5031

PR: https://git.openjdk.java.net/jdk/pull/5031