RFR: 8326370: Remove redundant and misplaced micros from StringBuffers

[Aleksey Shipilev]

On Tue, 20 Feb 2024 20:58:50 GMT, Claes Redestad <redestad at openjdk.org> wrote:

> Some microbenchmarks in org.openjdk.bench.java.lang.StringBuffers seem out-of-place (not testing `StringBuffer`), redundant (covered by other tests like StringSubstring or the various String concatenation tests), or both. This cleans them out. 
> 
> My apologies to Sigurd.

Marked as reviewed by shade (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/17937#pullrequestreview-1892606135