RFR: 7902766: Idempotent builds [v2]

[Jonathan Gibbons]

> 7902766: Idempotent builds
> In aid of idempotent builds ...
> 
> Replace `<delete>` before `<javac>` with `<depend>`
> Remove `<delete>` before copying help files
> 
> For now the <delete> tasks are just commented out. If you agree, they can be removed.

Jonathan Gibbons has updated the pull request incrementally with one additional commit since the last revision:

  remove <delete> lines

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

Changes:
  - all: https://git.openjdk.java.net/jtharness/pull/6/files
  - new: https://git.openjdk.java.net/jtharness/pull/6/files/6c24f76d..1951f3a6

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jtharness&pr=6&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jtharness&pr=6&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 2 del; 0 mod
  Patch: https://git.openjdk.java.net/jtharness/pull/6.diff
  Fetch: git fetch https://git.openjdk.java.net/jtharness pull/6/head:pull/6

PR: https://git.openjdk.java.net/jtharness/pull/6