Since #11100, in init.cpp `-blockmaxsize` is translated to `-blockmaxweight` with the code:

```
        unsigned int max_size = gArgs.GetArg("-blockmaxsize", 0);
        if (gArgs.SoftSetArg("blockmaxweight", strprintf("%d", max_size * WITNESS_SCALE_FACTOR))) {
```
However SoftSetArg requires the argument to be specified with the leading dash (ie, as `SoftSetArg("-blockmaxweight")`) without the dash the value will not be looked up later (because the later lookups specify it with a dash).

Obvious fix is just to add the dash (`SoftSetArg("-blockmaxweight", ...)`), but if there haven't been any complaints, just removing the option entirely might be better, since current behaviour is the same as if the option is just removed.

I believe this applies to master, 0.16 and 0.15 (due to backport via #11592).

Test case to demonstrate:

```
#!/usr/bin/env python3
"""Test limiting maxblocksize"""

from test_framework.test_framework import BitcoinTestFramework
from test_framework.util import *

class MaxBlockSizeTest(BitcoinTestFramework):
    def set_test_params(self):
        self.num_nodes = 2
        self.extra_args = [["-blockmaxweight=40000"], ["-blockmaxsize=10000"]]

    def run_test(self):
        chain_height = self.nodes[0].getblockcount()
        assert_equal(chain_height, 200)
        self.nodes[0].generate(100)
        self.nodes[1].generate(100)
        self.nodes[0].generate(100) # unspendable

        blk = [None,None]
        for n in [0,1]:
            vsize = 0
            address = self.nodes[n].getnewaddress()
            txes = 0
            while vsize*4 < 84000:
                txid = self.nodes[n].sendtoaddress(address, 0.25)
                tx = self.nodes[n].getrawtransaction(txid, 1)
                vsize += tx["vsize"]
                txes += 1
            self.nodes[n].generate(1)
            blk[n] = self.nodes[n].getblock(self.nodes[n].getbestblockhash())
            self.sync_all()

        assert blk[0]["weight"] <= 40000, "blockmaxweight greater than 40000"
        assert blk[1]["size"] <= 10000 or blk[1]["weight"] <= 40000, "blockmaxsize is greater than 10000"

if __name__ == '__main__':
    MaxBlockSizeTest().main()
```

Cc @jnewbery (who picked this up via an assertion failure in #11862) @TheBlueMatt (who did the original PR)
if (showDebug)
        strUsage += HelpMessageOpt("-rpcservertimeout=<n>", strprintf("Timeout during HTTP requests (default: %d)", DEFAULT_HTTP_SERVER_TIMEOUT));
    strUsage += HelpMessageOpt("-rpcthreads=<n>", strprintf(_("Set the number of threads to service RPC calls (default: %d)"), DEFAULT_HTTP_THREADS));
    strUsage += HelpMessageOpt("-rpcuser=<user>", _("Username for JSON-RPC connections"));
    if (showDebug)
        strUsage += HelpMessageOpt("-rpcworkqueue=<n>", strprintf("Set the depth of the work queue to service RPC calls (default: %d)", DEFAULT_HTTP_WORKQUEUE));
    strUsage += HelpMessageOpt("-server", _("Accept command line and JSON-RPC commands"));
    return strUsage;
}
std::string LicenseInfo()
{
    const std::string URL_SOURCE_CODE = "<https:github.com/bitcoin/bitcoin>";
    const std::string URL_WEBSITE = "<https:bitcoincore.org>";
    return CopyrightHolders(strprintf(_("Copyright (C) %i-%i"), 2009, COPYRIGHT_YEAR) + " ") + "\n" +
           "\n" +
           strprintf(_("Please contribute if you find %s useful. "
                       "Visit %s for further information about the software."),
               PACKAGE_NAME, URL_WEBSITE) +
           "\n" +
           strprintf(_("The source code is available from %s."),
               URL_SOURCE_CODE) +
           "\n" +
           "\n" +
           _("This is experimental software.") + "\n" +
           strprintf(_("Distributed under the MIT software license, see the accompanying file %s or %s"), "COPYING", "<https:opensource.org/licenses/MIT>") + "\n" +
           "\n" +
           strprintf(_("This product includes software developed by the OpenSSL Project for use in the OpenSSL Toolkit %s and cryptographic software written by Eric Young and UPnP software written by Thomas Bernard."), "<https:www.openssl.org>") +
           "\n";
}
static void BlockNotifyCallback(bool initialSync, const CBlockIndex *pBlockIndex)