CICD: Build: Remove conditional TOOLCHAIN logic

because we always use "stable". If we need to go back to using
matrix.job.toolchain, we should do it like in jobs.coverage, instead of
messing about with vars and outputs.

.github/workflows/CICD.yml

@@ -83,7 +83,7 @@ jobs:
       fail-fast: false
       matrix:
         job:
-          # { os, target, cargo-options, features, use-cross, toolchain }
+          # { os, target, cargo-options, features, use-cross }
           - { os: ubuntu-latest  , target: arm-unknown-linux-gnueabihf , use-cross: use-cross }
           - { os: ubuntu-18.04   , target: aarch64-unknown-linux-gnu   , use-cross: use-cross }
           - { os: ubuntu-18.04   , target: i686-unknown-linux-gnu      , use-cross: use-cross }
@@ -110,11 +110,6 @@ jobs:
       id: vars
       shell: bash
       run: |
-        # toolchain
-        TOOLCHAIN="stable" ## default to "stable" toolchain
-        # * use requested TOOLCHAIN if specified
-        if [ -n "${{ matrix.job.toolchain }}" ]; then TOOLCHAIN="${{ matrix.job.toolchain }}" ; fi
-        echo ::set-output name=TOOLCHAIN::${TOOLCHAIN}
         # staging directory
         STAGING='_staging'
         echo ::set-output name=STAGING::${STAGING}
@@ -194,7 +189,7 @@ jobs:
     - name: Install Rust toolchain
       uses: actions-rs/toolchain@v1
       with:
-        toolchain: ${{ steps.vars.outputs.TOOLCHAIN }}
+        toolchain: stable
         target: ${{ matrix.job.target }}
         override: true
         profile: minimal # minimal component installation (ie, no documentation)