RFR: 8344856: Remove calls to SecurityManager and doPrivileged in subclasses of URLConnection in the sun.net package after JEP 486 integration [v2]

[Volkan Yazıcı]

> This change set, addressing [8344856](https://bugs.openjdk.org/browse/JDK-8344856), removes `SecurityManager` and friends from `sun.net.www.protocol.ftp.FtpURLConnection`. This is the only leftover from `SM` cleanup in the subclasses of `URLConnection` in the `sun.net` package. Successful `tier1..3` CI runs on b02813b048ec63479c49e74ca6326a00409dd34f are shared in the ticket.

Volkan Yazıcı has updated the pull request incrementally with one additional commit since the last revision:

  Remove redundant suppression

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Changes:
  - all: https://git.openjdk.org/jdk/pull/22407/files
  - new: https://git.openjdk.org/jdk/pull/22407/files/44df905c..9b304657

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22407&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22407&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/22407.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22407/head:pull/22407

PR: https://git.openjdk.org/jdk/pull/22407