RFR: 8256325: Remove duplicate asserts in PhaseMacroExpand::expand_macro_nodes

[Tobias Hartmann]

[JDK-8239072](https://bugs.openjdk.java.net/browse/JDK-8239072) added a default case to the switch statement in PhaseMacroExpand::expand_macro_nodes:
https://hg.openjdk.java.net/jdk/jdk/rev/cf319f17c647#l3.67

This allows to merge the "expansion must have deleted one node from macro list" asserts and remove the duplicate asserts.

Thanks,
Tobias

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Commit messages:
 - 8256325: Remove duplicate asserts in PhaseMacroExpand::expand_macro_nodes

Changes: https://git.openjdk.java.net/jdk/pull/1200/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1200&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256325
  Stats: 5 lines in 1 file changed: 0 ins; 4 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1200.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1200/head:pull/1200

PR: https://git.openjdk.java.net/jdk/pull/1200