Remove deprecation mark on TGA texture format in lua_api.md

[corarona]

Add compact, short information about your PR for easier understanding:

• Goal of the PR
  To not make the api docs say tga is deprecated.

• How does the PR work?
  It removes the (deprecated) before .tga

• Does it resolve any reported issue?
  Yes. It partly resolves Remove TGA deprecation and put it in a ”do not deprecate again” list #13794

• Does this relate to a goal in the roadmap?
  I do not think so.

• If not a bug fix, why is this PR needed? What usecases does it solve?
  TGA was removed previously and then re-added. I do not see how the situation has changed since then.
  See Readd TGA to the list of valid texture formats. #11598 and Readd TGA format support irrlicht#64

TGA support is actively used in both mineclonia and mineclone2, it is also used by the tga_encoder, unicode_text and my recent unicode_signs mod which uses the former 2.

If anything .bmp should be removed and not tga, which would save a lot more code as well if I understand it right (which I maybe do not).

How to test

• Read the lua_api.md in master and be shocked by the fact that TGA is marked as deprecated.
• Read it again on this branch and rejoice in the fact that the deprecation mark was removed.

[sfan5]

FWIW the coredev opinion on this seems to be mostly neutral/positive (except me) so I don't know if "controversial" is warranted.

[erlehmann]

TGA was removed previously and then re-added. I do not see how the situation has changed since then.

If anything, more mods use TGA now than back then.

Btw, just in case anyone comes across this PR in the future and does not want to ponder it too much: The decision whether to deprecate TGA or not, beyond compatibility concerns, is pretty much “Does Minetest want to support an image format that is easy to write and read from Lua or not?” (i.e. can you roundtrip an image by decoding and encoding it or not).

Given the presence of minimum-effort PNG encoding capabilities and complete lack of image reading capabilities in the Minetest engine, I believe that the decision basically comes down to “Should Minetest mods be easily able to edit textures loaded from files (or item meta)?”. I think they should, so that e.g. handheld maps can be (sort of) live-updated, zoomed out and combined.

[SmallJoker]

Fine by me.

[celeron55]

At this point I will give my +1 to this.

The arguments against it are mostly about the potential maintenance burden, and the arguments for it are mostly about preference and ease of use. It's difficult to predict how much work maintenance will require, but it is a relatively simple format which could mean it's simple to maintain, and I am in general a proponent of simple easy to use things.

In general we should be happy MT has a feature someone likes this much.

[erlehmann]

Please remember to merge this before the release to prevent confusion.