Incorrect and duplicate terrain textures

[historic_bruno]

All the following textures are duplicate named DDS+PNG terrain textures found by checkrefs.pl.

Some of the DDS are outdated and should probably be removed:

binaries/data/mods/public/art/textures/terrain/types/alpine_grass_a.dds
binaries/data/mods/public/art/textures/terrain/types/alpine_grass_b.dds
binaries/data/mods/public/art/textures/terrain/types/alpine_grass_c.dds
binaries/data/mods/public/art/textures/terrain/types/alpine_grass_d.dds

Normal map when it should be diffuse:

binaries/data/mods/public/art/textures/terrain/types/desert_forestfloor_palms.png

Low quality copy of DDS:

binaries/data/mods/public/art/textures/terrain/types/snow grass 2.png

[historic_bruno]

Actually, ignore art/textures/terrain/types/grass1_spring.dds because that one is special. The PNG version has alpha and gets used for myconid's experimental fancy grass effect.

[ben]

In 13693:

Renames confusing grass1_spring.png terrain texture, used for fancy grass effect, refs #2069

[michael]

I'll look into these.

[michael]

In 13738:

Fixes #2069.