RFR: 8255416: Investigate err_msg to detect unnecessary uses [v4]

[Anton Kozlov]

> Hi,
> 
> When a single string without formatting arguments is provided to `err_msg`, it's redundancy, as the same message could be used without any err_msg. This is a follow-up to the discussion https://github.com/openjdk/jdk/pull/812#discussion_r511784050
> 
> Please review a change that makes `err_msg` with a single string to fail compilation. 
> 
> Detected uses of err_msg with a single string were eliminated as well.

Anton Kozlov has updated the pull request incrementally with two additional commits since the last revision:

 - Unlink err_msg interface from FormatBuffer
 - Remove implementation of the dummy ctor

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/905/files
  - new: https://git.openjdk.java.net/jdk/pull/905/files/8a99cdcc..47ff851e

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=905&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=905&range=02-03

  Stats: 11 lines in 4 files changed: 4 ins; 0 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/905.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/905/head:pull/905

PR: https://git.openjdk.java.net/jdk/pull/905