RFR: 8278143: Remove unused "argc" from ConstantPool::copy_bootstrap_arguments_at_impl

[Aleksey Shipilev]

SonarCloud complains about variable initialization in large conditional statements. In that tower of if-expressions, it is not even clear to me that `argc` would be properly initialized. Seems better to clean that up.

Additional testing:
 - [x] Linux x86_64 fastdebug build
 - [ ] GHA

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Commit messages:
 - Fix

Changes: https://git.openjdk.java.net/jdk/pull/6671/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6671&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278143
  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6671.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6671/head:pull/6671

PR: https://git.openjdk.java.net/jdk/pull/6671