ci: Don't set compiler-builtins-no-f16-f128

Since rust-lang/rust be35d37d8b6c ("Use the compiler to determine
whether or not to enable f16 and f128"), `compiler-builtins` relies on
`rustc` to report whether or not `f16` and `f128` are supported, which
is reported by the backend. This means that there should no longer be
any need to set this config in CI.

Backend config: https://github.com/rust-lang/rustc_codegen_gcc/blob/f682d09eefc6700b9e5851ef193847959acf4fac/src/lib.rs#L499-L510

Author: tgross35

.github/workflows/m68k.yml

@@ -82,14 +82,14 @@ jobs:
     - name: Build sample project with target defined as JSON spec
       run: |
         ./y.sh prepare --only-libcore --cross
-        ./y.sh build --sysroot --features compiler-builtins-no-f16-f128 --target-triple m68k-unknown-linux-gnu --target ${{ github.workspace }}/target_specs/m68k-unknown-linux-gnu.json
+        ./y.sh build --sysroot --target-triple m68k-unknown-linux-gnu --target ${{ github.workspace }}/target_specs/m68k-unknown-linux-gnu.json
         CG_RUSTFLAGS="-Clinker=m68k-unknown-linux-gnu-gcc" ./y.sh cargo build --manifest-path=./tests/hello-world/Cargo.toml --target ${{ github.workspace }}/target_specs/m68k-unknown-linux-gnu.json
         ./y.sh clean all
 
     - name: Build
       run: |
         ./y.sh prepare --only-libcore --cross
-        ./y.sh build --sysroot --features compiler-builtins-no-f16-f128 --target-triple m68k-unknown-linux-gnu
+        ./y.sh build --sysroot --target-triple m68k-unknown-linux-gnu
         ./y.sh test --mini-tests --target-triple m68k-unknown-linux-gnu
         CG_GCC_TEST_TARGET=m68k-unknown-linux-gnu ./y.sh test --cargo-tests --target-triple m68k-unknown-linux-gnu
         ./y.sh clean all
@@ -102,7 +102,7 @@ jobs:
 
     - name: Run tests
       run: |
-        ./y.sh test --target-triple m68k-unknown-linux-gnu --release --clean --build-sysroot --sysroot-features compiler-builtins-no-f16-f128 ${{ matrix.commands }}
+        ./y.sh test --target-triple m68k-unknown-linux-gnu --release --clean --build-sysroot ${{ matrix.commands }}
 
     - name: Run Hello World!
       run: |