Update default assume valid and minimum chain work params

These have been updated according to contrib/devtools/chainparams/README.md.

The assumed valid block for scalenet is left unchanged (9,999 - just below the
planned re-org height of 10,000).

For all other *test* networks, the assumed valid block is still 2,000
below the chain tip at the time of running the make_chainparams script.

For mainnet, it's 10 blocks below chain tip.
Here: mainnet block : 699484

Test plan:
- review (confirm assume hashes using block explorer)
  - note that the minchainwork is +10 (for main) or +2000 blocks from
    that given hash.
- `ninja check`

contrib/devtools/chainparams/chainparams_main.txt

@@ -1,2 +1,2 @@
-000000000000000000673d4febaa98e967d9f1df911f3665e2495285e9c3a82d
-0000000000000000000000000000000000000000016480e5f464ea2e12e68a38
+0000000000000000030192242425926218184a609a63efee615b7586d7f3972b
+000000000000000000000000000000000000000001768829963ed323dbfcc190

contrib/devtools/chainparams/chainparams_test.txt

@@ -1,2 +1,2 @@
-00000000005b186499815695637db45afa07d3227fff5614be8bd969e8351846
-000000000000000000000000000000000000000000000071855a176dfa32d62e
+000000000075b31cf81de7986358fca0d007309232e779eaef3ca479825a8664
+0000000000000000000000000000000000000000000000735672b6c8d71e440f

contrib/devtools/chainparams/chainparams_testnet4.txt

@@ -1,2 +1,2 @@
-000000000031fca3b085008f5c8c7b195e293632f11f7ea2fe512744a5aca8cd
-00000000000000000000000000000000000000000000000000b957a9d5efce1f
+000000000042458f9dd6b5ebae4574ed157c89e4c7126e1eb53263fe71c09786
+00000000000000000000000000000000000000000000000000fe5e402a2d2364

src/chainparamsconstants.h

@@ -9,14 +9,14 @@
 #include <uint256.h>
 
 namespace ChainParamsConstants {
-    const BlockHash MAINNET_DEFAULT_ASSUME_VALID = BlockHash::fromHex("000000000000000000673d4febaa98e967d9f1df911f3665e2495285e9c3a82d");
-    const uint256 MAINNET_MINIMUM_CHAIN_WORK = uint256S("0000000000000000000000000000000000000000016480e5f464ea2e12e68a38");
+    const BlockHash MAINNET_DEFAULT_ASSUME_VALID = BlockHash::fromHex("000000000000000000e7f24c197edd6de599d77fc837f630b6f4c6259dfeb4dd");
+    const uint256 MAINNET_MINIMUM_CHAIN_WORK = uint256S("000000000000000000000000000000000000000001765b047f3c2b0e03d74000");
 
-    const BlockHash TESTNET_DEFAULT_ASSUME_VALID = BlockHash::fromHex("00000000005b186499815695637db45afa07d3227fff5614be8bd969e8351846");
-    const uint256 TESTNET_MINIMUM_CHAIN_WORK = uint256S("000000000000000000000000000000000000000000000071855a176dfa32d62e");
+    const BlockHash TESTNET_DEFAULT_ASSUME_VALID = BlockHash::fromHex("00000000002e38a0fb71cba3698b4787c9755156668e86dbf495fcd2489b6c62");
+    const uint256 TESTNET_MINIMUM_CHAIN_WORK = uint256S("000000000000000000000000000000000000000000000073552e09a3b8e92bd5");
 
-    const BlockHash TESTNET4_DEFAULT_ASSUME_VALID = BlockHash::fromHex("000000000031fca3b085008f5c8c7b195e293632f11f7ea2fe512744a5aca8cd");
-    const uint256 TESTNET4_MINIMUM_CHAIN_WORK = uint256S("00000000000000000000000000000000000000000000000000b957a9d5efce1f");
+    const BlockHash TESTNET4_DEFAULT_ASSUME_VALID = BlockHash::fromHex("00000000000b80e19dfd5e1fe093aa03b7e9d6cb8ce7637de1f2ecbd882bdfeb");
+    const uint256 TESTNET4_MINIMUM_CHAIN_WORK = uint256S("00000000000000000000000000000000000000000000000000fd01607cbee7e6");
 
     // Scalenet re-organizes above height 10,000 - use block 9,999 hash here.
     const BlockHash SCALENET_DEFAULT_ASSUME_VALID = BlockHash::fromHex("000000007fb3362740efd1435aa414f54171993483799782f83c61bc7bf1b1be");