[libc++][CI] Don't install libc6-dev-i386 in the Docker image

We don't cross-compile to 32 bits in the CI anymore.

Author: ldionne

libcxx/utils/ci/Dockerfile

@@ -43,7 +43,6 @@ RUN apt-get update && apt-get install -y bash curl
 
 # Install various tools used by the build or the test suite
 RUN apt-get update && apt-get install -y ninja-build python3 python3-sphinx python3-distutils git gdb
-RUN apt-get update && apt-get install -y libc6-dev-i386 # Required to cross-compile to 32 bits
 
 # Locales for gdb and localization tests
 RUN apt-get update && apt-get install -y language-pack-en language-pack-fr \