RFR: 8277797: Remove undefined/unused SharedRuntime::trampoline_size()

[Zhengyu Gu]

A trivial patch to remove undefined and unused `SharedRuntime::trampoline_size()`, a leftover from [JDK-8263002](https://bugs.openjdk.java.net/browse/JDK-8263002).

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Commit messages:
 - v0

Changes: https://git.openjdk.java.net/jdk/pull/6540/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6540&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8277797
  Stats: 2 lines in 1 file changed: 0 ins; 2 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6540.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6540/head:pull/6540

PR: https://git.openjdk.java.net/jdk/pull/6540