scripted-diff: Use BlockManager::LookupBlockIndex

[META] In a previous commit, we moved ::LookupBlockIndex to become a
       member function of BlockManager. This commit is split out from
       that one since it can be expressed nicely as a scripted-diff.

-BEGIN VERIFY SCRIPT-
find_regex='LookupBlockIndex' \
    && git grep -l -E "$find_regex" -- src \
        | grep -v '^src/validation\.\(cpp\|h\)$' \
        | xargs sed -i -E "s@${find_regex}@g_chainman.m_blockman.LookupBlockIndex@g"
-END VERIFY SCRIPT-

src/init.cpp

@@ -1611,7 +1611,7 @@ bool AppInitMain(const util::Ref& context, NodeContext& node, interfaces::BlockA
                 // If the loaded chain has a wrong genesis, bail out immediately
                 // (we're likely using a testnet datadir, or the other way around).
                 if (!chainman.BlockIndex().empty() &&
-                        !LookupBlockIndex(chainparams.GetConsensus().hashGenesisBlock)) {
+                        !g_chainman.m_blockman.LookupBlockIndex(chainparams.GetConsensus().hashGenesisBlock)) {
                     return InitError(_("Incorrect or no genesis block found. Wrong datadir for network?"));
                 }