This commit adds a ProcessImportLegacy() function which
currently does nothing. It also unindents a block of
code for a future move-only change.
Reviewer hint: review with -w to ignore whitespace changes.
This is a partial backport of Core PR14491 : https://github.com/bitcoin/bitcoin/pull/14491/commits/4cac0ddd258bc82258ccc99568d02d3b2415339d