Remove git submodules that will be loaded through conan

.gitmodules

@@ -1,54 +1,30 @@
 [submodule "inih"]
     path = externals/inih/inih
     url = https://github.com/svn2github/inih
-[submodule "boost"]
-    path = externals/boost
-    url = https://github.com/yuzu-emu/ext-boost.git
-[submodule "catch"]
-    path = externals/catch
-    url = https://github.com/philsquared/Catch.git
 [submodule "cubeb"]
     path = externals/cubeb
     url = https://github.com/kinetiknz/cubeb.git
 [submodule "dynarmic"]
     path = externals/dynarmic
     url = https://github.com/MerryMage/dynarmic.git
-[submodule "fmt"]
-    path = externals/fmt
-    url = https://github.com/fmtlib/fmt.git
-[submodule "lz4"]
-    path = externals/lz4
-    url = https://github.com/lz4/lz4.git
 [submodule "unicorn"]
     path = externals/unicorn
     url = https://github.com/yuzu-emu/unicorn
-[submodule "mbedtls"]
-    path = externals/mbedtls
-    url = https://github.com/DarkLordZach/mbedtls
-[submodule "opus"]
-    path = externals/opus/opus
-    url = https://github.com/xiph/opus.git
 [submodule "soundtouch"]
     path = externals/soundtouch
     url = https://github.com/citra-emu/ext-soundtouch.git
-[submodule "libressl"]
-    path = externals/libressl
-    url = https://github.com/citra-emu/ext-libressl-portable.git
 [submodule "discord-rpc"]
     path = externals/discord-rpc
     url = https://github.com/discordapp/discord-rpc.git
 [submodule "Vulkan-Headers"]
     path = externals/Vulkan-Headers
     url = https://github.com/KhronosGroup/Vulkan-Headers.git
-[submodule "externals/zstd"]
-    path = externals/zstd
-    url = https://github.com/facebook/zstd
 [submodule "sirit"]
     path = externals/sirit
     url = https://github.com/ReinUsesLisp/sirit
+[submodule "mbedtls"]
+    path = externals/mbedtls
+    url = https://github.com/DarkLordZach/mbedtls
 [submodule "libzip"]
     path = externals/libzip/libzip
     url = https://github.com/nih-at/libzip.git
-[submodule "zlib"]
-    path = externals/zlib/zlib
-    url = https://github.com/madler/zlib.git