RFR: CODETOOLS-7903010: Delete obsolete build-all.sh and README-v5 files

[Jonathan Gibbons]

Two files related to the previous iteration of the build system are deleted.

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

Commit messages:
 - CODETOOLS-7903010: Delete obsolete build-all.sh and README-v5 files

Changes: https://git.openjdk.java.net/jtreg/pull/23/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jtreg&pr=23&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7903010
  Stats: 513 lines in 2 files changed: 0 ins; 513 del; 0 mod
  Patch: https://git.openjdk.java.net/jtreg/pull/23.diff
  Fetch: git fetch https://git.openjdk.java.net/jtreg pull/23/head:pull/23

PR: https://git.openjdk.java.net/jtreg/pull/23