RFR: 8267317: Remove DeferredTypeCompleter

Tue May 18 13:01:57 UTC 2021

This pathc removes DeferredTypeCompleter, which seems like a dubious abstraction. In its place there is now a `complete` method on `DeferredType` which is overridden by `ArgumentType`. The only problematic usage is from `StructuralStuckChecker`, but after inspecting the code I realized that the only side effect this code expected from calling `DeferredType::check` was to set the deferred type mode to `SPECULATIVE`, which we can easily do inline.

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Commit messages:
 - All tests pass

Changes: https://git.openjdk.java.net/jdk/pull/4091/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4091&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267317
  Stats: 81 lines in 2 files changed: 18 ins; 49 del; 14 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4091.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4091/head:pull/4091

PR: https://git.openjdk.java.net/jdk/pull/4091