docker: remove useless cargo install with apt (#14636)

Signed-off-by: Mathieu Velten <mathieuv@matrix.org>

changelog.d/14636.misc

@@ -0,0 +1 @@
+Remove useless cargo install with apt from Dockerfile.

docker/Dockerfile

@@ -43,7 +43,7 @@ RUN \
    --mount=type=cache,target=/var/cache/apt,sharing=locked \
    --mount=type=cache,target=/var/lib/apt,sharing=locked \
     apt-get update -qq && apt-get install -yqq \
-      build-essential cargo git libffi-dev libssl-dev \
+      build-essential git libffi-dev libssl-dev \
     && rm -rf /var/lib/apt/lists/*
 
 # We install poetry in its own build stage to avoid its dependencies conflicting with