[CSL-875] Redefine 'staticSysStart' via 'isDevelopment'
[CSL-875] Redefine 'staticSysStart' via 'isDevelopment'

Previously 'staticSysStart' used "#ifdef DEV_MODE" and 'isDevelopment' was
defined as "isNothing staticSysStart". That was pretty weird. Now
'isDevelopment' is defined via "#ifdef DEV_MODE" and 'staticSysStart' uses 'isDevelopment'.

input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype,input-output-hk/pos-haskell-prototype