[validation] Move validation-only consts to validation.cpp

Summary:
This is a backport of Core PR17383 [2/4]
https://github.com/bitcoin/bitcoin/pull/17383/commits/0109622b08887ed01a30911477ce4b8f266d4b4a
Depends on D8976

UNDOFILE_CHUNK_SIZE and BLOCKFILE_CHUNK_SIZE were moved to blockdb.h in
D7579
MAX_DISCONNECTED_TX_POOL_SIZE was moved to txmempool.h on D1667

MAX_FEE_ESTIMATION_TIP_AGE is unused since D2784

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D8977