BIP8: remove redundant and conflicting sentence from param selection

At the end of the param selection section it's explicitly stated that
startheight _must_ be a multiple of 2016.

bip-0008.mediawiki

@@ -47,7 +47,7 @@ The following guidelines are suggested for selecting these parameters for a soft
 
 # '''name''' should be selected such that no two softforks, concurrent or otherwise, ever use the same name. For deployments described in a single BIP, it is recommended to use the name "bipN" where N is the appropriate BIP number.
 # '''bit''' should be selected such that no two concurrent softforks use the same bit. The bit chosen should not overlap with active usage (legitimately or otherwise) for other purposes.
-# '''startheight''' should be set to some block height in the future when a majority of economic activity is expected to have upgraded to a software release including the activation parameters. Some allowance should be made for potential release delays. It should be rounded up to the next height which begins a retarget period for simplicity.
+# '''startheight''' should be set to some block height in the future when a majority of economic activity is expected to have upgraded to a software release including the activation parameters. Some allowance should be made for potential release delays.
 # '''timeoutheight''' should be set to a block height when it is considered reasonable to expect the entire economy to have upgraded by, probably at least 1 year, or 52416 blocks (26 retarget intervals) after '''startheight'''.
 # '''threshold''' should be 1815 blocks (90% of 2016), or 1512 (75%) for testnet.
 # '''lockinontimeout''' should be set to true for any softfork that is expected or found to have political opposition from a non-negligible percent of miners. (It can be set after the initial deployment, but cannot be cleared once set.)