RFR: JDK-8280373: adjust other SystemIDResolver.java after 8270492

[Matthias Baesken]

After 8270492
https://github.com/openjdk/jdk/commit/78b2c8419bc69436873e6fc9c542480949d140c5
has been pushed, we should adjust src/java.xml/share/classes/com/sun/org/apache/xml/internal/serializer/utils/SystemIDResolver.java getAbsoluteURI to what has been done in 8270492 to src/java.xml/share/classes/com/sun/org/apache/xml/internal/utils/SystemIDResolver.java

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Commit messages:
 - JDK-8280373

Changes: https://git.openjdk.java.net/jdk/pull/7155/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7155&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280373
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7155.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7155/head:pull/7155

PR: https://git.openjdk.java.net/jdk/pull/7155