[crypto] Remove CI check against mbedTLS 2.x

Signed-off-by: Łukasz Duda <lukasz.duda@nordicsemi.no>

Author: LuDuda

.github/workflows/build.yml

@@ -188,8 +188,11 @@ jobs:
       run: |
         script/check-scan-build
 
-  mbedtls2-build:
+  mbedtls3-build:
     runs-on: ubuntu-24.04
+    env:
+      CFLAGS: -DCOPENTHREAD_CONFIG_CRYPTO_LIB=OPENTHREAD_CONFIG_CRYPTO_LIB_MBEDTLS -DOPENTHREAD_CONFIG_PLATFORM_KEY_REFERENCES_ENABLE=0
+      CXXFLAGS: -DCOPENTHREAD_CONFIG_CRYPTO_LIB=OPENTHREAD_CONFIG_CRYPTO_LIB_MBEDTLS -DOPENTHREAD_CONFIG_PLATFORM_KEY_REFERENCES_ENABLE=0
     steps:
     - name: Harden Runner
       uses: step-security/harden-runner@0080882f6c36860b6ba35c610c98ce87d4e2f26f # v2.10.2
@@ -202,12 +205,6 @@ jobs:
     - name: Bootstrap
       run: |
         sudo apt-get --no-install-recommends install -y ninja-build libreadline-dev libncurses-dev
-        rm -rf third_party/mbedtls/repo
-    - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
-      with:
-        repository: ARMmbed/mbedtls
-        ref: v2.28.8
-        path: third_party/mbedtls/repo
     - name: Build
       run: |
         ./script/test build