Remove unused org.eclipse.swt.gtk.linux.loongarch64 fragment

[HannesWell]

It is neither built nor published and currently just dead configuration that still needs to be updated regularly.

And the last attempt to make it work was abandoned in

• Updated the code related to LoongArch and added the necessary so files. #1135

If desired, it can be added back at any time.

[github-actions]

Test Results

  188 files  ±0    188 suites  ±0   27m 31s ⏱️ + 1m 44s
4 732 tests ±0  4 709 ✅ ±0   23 💤 ±0  0 ❌ ±0 
6 861 runs  ±0  6 698 ✅ ±0  163 💤 ±0  0 ❌ ±0 

Results for commit 43812d3. ± Comparison against base commit f49428e.

♻️ This comment has been updated with latest results.

[HeikoKlare]

I am fine with removing this fragment.

I see some places that should probably be adapted as well:

• Agents.md information about the architecture being supported:

  eclipse.platform.swt/AGENTS.md

  Line 46 in f49428e

  - **Supported Architectures**: x86_64, aarch64, loongarch64, ppc64le, riscv64

• Architecture being mentioned in the readme:

  eclipse.platform.swt/bundles/org.eclipse.swt/Readme.md

  Lines 25 to 26 in f49428e

  	These examples refer to the architecture `x86_64` but there are other projects for
  	other architectures, like `aarch64` (or `loongarch64` / `ppc64le` for Linux).

• Binaries build script case for the architecture:

  eclipse.platform.swt/bundles/org.eclipse.swt/Eclipse SWT PI/gtk/library/build.sh

  Lines 130 to 137 in f49428e

  	"linux.loongarch64")
  	if [ "${CC}" = "" ]; then
  	export CC=gcc
  	fi
  	if [ "${PKG_CONFIG_PATH}" = "" ]; then
  	export PKG_CONFIG_PATH="/usr/lib64/pkgconfig/"
  	fi
  	;;