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/rest.cpp

@@ -179,7 +179,7 @@ static bool rest_headers(const util::Ref& context,
     {
         LOCK(cs_main);
         tip = ::ChainActive().Tip();
-        const CBlockIndex* pindex = LookupBlockIndex(hash);
+        const CBlockIndex* pindex = g_chainman.m_blockman.LookupBlockIndex(hash);
         while (pindex != nullptr && ::ChainActive().Contains(pindex)) {
             headers.push_back(pindex);
             if (headers.size() == (unsigned long)count)
@@ -247,7 +247,7 @@ static bool rest_block(HTTPRequest* req,
     {
         LOCK(cs_main);
         tip = ::ChainActive().Tip();
-        pblockindex = LookupBlockIndex(hash);
+        pblockindex = g_chainman.m_blockman.LookupBlockIndex(hash);
         if (!pblockindex) {
             return RESTERR(req, HTTP_NOT_FOUND, hashStr + " not found");
         }