RFR: 8307553: Remove dead code MetaspaceClosure::push_method_entry

[Ioi Lam]

Please review this trivial change to remove dead code, which is unused since [JDK-8263002](https://bugs.openjdk.org/browse/JDK-8263002), when CDS method trampolines were removed.

-------------

Commit messages:
 - 8307553: Remove dead code MetaspaceClosure::push_method_entry

Changes: https://git.openjdk.org/jdk/pull/13842/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13842&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8307553
  Stats: 66 lines in 3 files changed: 0 ins; 66 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13842.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13842/head:pull/13842

PR: https://git.openjdk.org/jdk/pull/13842