ci: remove deprecated input

Signed-off-by: Frederic Pillon <frederic.pillon@st.com>

Author: fpistm

.github/workflows/Continuous-Integration.yml

@@ -31,7 +31,6 @@ jobs:
       with:
         custom-config: "./extras/rtc_cores_config.json"
         additional-url: 'https://github.com/stm32duino/BoardManagerFiles/raw/dev/package_stmicroelectronics_index.json'
-        use-core-repo: 'true'
 
     # Use the output from the `Compile` step
     - name: Compilation Errors