GUI: Options: Remove the upper-bound limit from pruning size setting
GUI: Options: Remove the upper-bound limit from pruning size setting

Hypothetically, someone may wish to begin pruning at a future blockchain size, and there's no reason to limit it lower

Github-Pull: #15801
Rebased-From: 8a33f4d63f9944f4877b3e2814b1582e72ceaa71
Tree-SHA512: 814dc5f004c3418216a12f8e0ef1a8db2c586d98b515d48b31a8ccd7f4e0deb12b9f2b6110bf702576a32802ca1d30e518df5ad7c28046deb4d0e9be46a6e7b8

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