Oddities in single-point mapalgo defaults

Various `mapalgo` settings are bilinear by default, with some single-point sites set to nearest-neighbor. It's not clear:
- Why those sites are set to nearest-neighbor
- Why other sites aren't

`popdensmapalgo` has some sites missing (e.g., `1x1_smallvilleIA`):

https://github.com/ESCOMP/CTSM/blob/a9433779f0ae499d60ad118d2ec331628f0eaaa8/bld/namelist_files/namelist_defaults_ctsm.xml#L1818-L1825

Same for `lightngmapalgo`:

https://github.com/ESCOMP/CTSM/blob/a9433779f0ae499d60ad118d2ec331628f0eaaa8/bld/namelist_files/namelist_defaults_ctsm.xml#L1724-L1731

Same for `urbantvmapalgo`:

https://github.com/ESCOMP/CTSM/blob/a9433779f0ae499d60ad118d2ec331628f0eaaa8/bld/namelist_files/namelist_defaults_ctsm.xml#L1877-L1884

`lai_mapalgo` has some sites repeated (e.g., `1x1_brazil`) and some sites missing (e.g., `1x1_smallvilleIA`):

https://github.com/ESCOMP/CTSM/blob/a9433779f0ae499d60ad118d2ec331628f0eaaa8/bld/namelist_files/namelist_defaults_ctsm.xml#L1674-L1687