Unused strings noted during build

[jonathanolson]

See code review: https://github.com/phetsims/build-a-molecule/issues/173

The strings in question:

>> Unused string: key=hydrogenPeroxide, value=Hydrogen Peroxide
>> Unused string: key=formaldehyde, value=Formaldehyde
>> Unused string: key=silane, value=Silane
>> Unused string: key=water, value=Water
>> Unused string: key=borane, value=Borane
>> Unused string: key=hydrogenSulfide, value=Hydrogen Sulfide
>> Unused string: key=carbonDioxide, value=Carbon Dioxide
>> Unused string: key=chloromethane, value=Chloromethane
>> Unused string: key=ballAndStick, value=Ball and Stick
>> Unused string: key=phosphine, value=Phosphine
>> Unused string: key=sulfurDioxide, value=Sulfur Dioxide
>> Unused string: key=ozone, value=Ozone
>> Unused string: key=fluoromethane, value=Fluoromethane
>> Unused string: key=resetCollection, value=Reset Collection
>> Unused string: key=spaceFilling, value=Space Filling
>> Unused string: key=hydrogenCyanide, value=Hydrogen Cyanide
>> Unused string: key=acetylene, value=Acetylene
>> Unused string: key=kitPattern, value=Kit #{{number}}
>> Unused string: key=trifluoroborane, value=Trifluoroborane
>> Unused string: key=carbonMonoxide, value=Carbon Monoxide
>> Unused string: key=methane, value=Methane
>> Unused string: key=ammonia, value=Ammonia
>> Unused string: key=ethylene, value=Ethylene
>> Unused string: key=nitrousOxide, value=Nitrous Oxide
>> Unused string: key=nitricOxide, value=Nitric Oxide
>> Unused string: key=refill, value=Refill

[Denz1994]

Unused strings were removed from the strings.json. Running grunt isn't reporting any unused strings any longer.