RFR: JDK-8296235: IGV: Change shortcut to delete graph from ctrl+del to del

[Tobias Holenstein]

Change the current shortcut to delete a graph from `ctrl`+`delete` to `delete` only (dropping ctrl).

For keyboards without the `delete` key (like Mac) the alternative shortcut `ctrl`+`backspace` is unchanged

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Commit messages:
 - JDK-8296235: IGV: Change shortcut to delete graph from ctrl+del to del

Changes: https://git.openjdk.org/jdk/pull/10950/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10950&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296235
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/10950.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10950/head:pull/10950

PR: https://git.openjdk.org/jdk/pull/10950