This removes around megabyte from the binary, so a stripped -Og binary
went from 4.0 megabytes to 2.9 megabytes, and an unstripped -O0 binary
went from 8.1 megabytes to 7.1 megabytes, which means I can now finally
upload an unstripped -O0 binary to Discord without having to give money
to Discord for their dumb Nitro thing or whatever.
Following discussion on TerryCavanagh/VVVVVV#153, I suggested that
instead of reverting my M&P guards from TerryCavanagh/VVVVVV#124 (which
would only revert it for The Final Level, The Lab, Overworld, and The
Tower, leaving Space Station 1 & 2 and The Warp Zone alone which could
potentially cause the same problem that motivated
TerryCavanagh/VVVVVV#153), we should initialize the map data with 0s
instead.
This is to make sure that the room data of those areas are not
distributed with the M&P binary, even if they are already inaccessible
because of other M&P ifdefs (I tested).
