Fix plArmatureLODMod writing PRC Meshes tag twice

[dgelessus]

The base class plArmatureModBase already writes the Meshes tag, so plArmatureLODMod shouldn't write it a second time.

[dpogue]

LGTM

[zrax]

Ugh. These appear to be duplicated because the stream I/O also has duplicate readers and writers for them... There's nothing we can do about the stream format without breaking existing PRPs, but yeah, it makes sense to at least clean up the PRC output.

[dgelessus]

These appear to be duplicated because the stream I/O also has duplicate readers and writers for them...

Actually, nothing is duplicated in the stream data either - but
the code is really wacky here. There are two places that read the meshes (plArmatureModBase::read and plArmatureLODMod::read), but only the latter is actually executed. Note that (for Uru PRPs) plArmatureMod::read doesn't call the base class method plArmatureModBase::read, but instead skips one class up the chain to plAGMasterMod::read. So one of the two places where the meshes are read is always skipped. The same thing happens when writing.

The trouble was that the PRC read/write code replicated one half of this wacky logic (two classes reading/writing the same field), but not the other half (skipping one of those two implementations).