Supprime la branche nalc de plusieurs sous-modules

sea, slimes, nether

.gitmodules

@@ -358,15 +358,12 @@
 [submodule "sea"]
 	path = sea
 	url = https://sys4.fr/gitea/nalc/minetest-mod-sea.git
-	branch = nalc
 [submodule "slimes"]
 	path = slimes
 	url = https://sys4.fr/gitea/nalc/mod-slimes.git
-	branch = nalc
 [submodule "nether"]
 	path = nether
 	url = https://sys4.fr/gitea/nalc/nether-pack.git
-	branch = nalc
 [submodule "colddb"]
 	path = colddb
 	url = https://sys4.fr/gitea/nalc/colddb.git