[code-reflection] RFR: Cleanup compiler code gen

[Paul Sandoz]

Remove option for storing the model as text now the alternative is stable (retain the enum for when we experiment with further kinds of encoding).

Change the code extracting the Quoted instance from a structurally quoted lambda to not use the interpreter.

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Commit messages:
 - Cleanup compiler code gen

Changes: https://git.openjdk.org/babylon/pull/471/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=471&range=00
  Stats: 60 lines in 3 files changed: 7 ins; 32 del; 21 mod
  Patch: https://git.openjdk.org/babylon/pull/471.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/471/head:pull/471

PR: https://git.openjdk.org/babylon/pull/471