AP_GPS: remove dedundant crc32 routine from Nova

[peterbarker]

Relying on the simulator to test this

[amilcarlucas]

Binary Name      Text [B]        Data [B]     BSS (B)        Total Flash Change [B] (%)      Flash Free After PR (B)
---------------  --------------  -----------  -------------  ----------------------------  -------------------------
arducopter-heli  -76 (-0.0043%)  0 (0.0000%)  4 (+0.0015%)   -76 (-0.0042%)                                   176932
antennatracker   -76 (-0.0057%)  0 (0.0000%)  4 (+0.0015%)   -76 (-0.0057%)                                   637456
arduplane        -76 (-0.0043%)  0 (0.0000%)  -4 (-0.0015%)  -76 (-0.0043%)                                   183660
arducopter       -76 (-0.0043%)  0 (0.0000%)  -4 (-0.0015%)  -76 (-0.0043%)                                   183276
ardurover        -76 (-0.0046%)  0 (0.0000%)  -4 (-0.0015%)  -76 (-0.0046%)                                   328944
blimp            -76 (-0.0056%)  0 (0.0000%)  -4 (-0.0015%)  -76 (-0.0056%)                                   614404
ardusub          -76 (-0.0048%)  0 (0.0000%)  -4 (-0.0015%)  -76 (-0.0048%)                                   388708