RFR: 8278494: Remove .hgtags

[Kevin Rushforth]

Trivial fix to remove the obsolete `.hgtags` file from the repo. As mentioned in JBS, this file has (intentionally) not been updated since the switch to git. It will continue to be available in the `jfx17` branch [here](https://github.com/openjdk/jfx/blob/jfx17/.hgtags). The corresponding file was recently removed from the `jdk` repo.

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Commit messages:
- 8278494: Remove .hgtags

Changes: https://git.openjdk.java.net/jfx/pull/691/files
Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=691&range=00
Issue: https://bugs.openjdk.java.net/browse/JDK-8278494
Stats: 544 lines in 1 file changed: 0 ins; 544 del; 0 mod
Patch: https://git.openjdk.java.net/jfx/pull/691.diff
Fetch: git fetch https://git.openjdk.java.net/jfx pull/691/head:pull/691

PR: https://git.openjdk.java.net/jfx/pull/691