docker: drop fftw too -- the project builds FFTW itself

FFTW is fetched and built by the jungfraujoch CMake (single-precision, from the
release tarball), so the system fftw packages (fftw-static/fftw-devel on Rocky,
libfftw3-dev on Ubuntu) were unused. Remove them from all four images.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docker/rocky8/Dockerfile

@@ -52,8 +52,6 @@ RUN dnf -y update && \
       zlib-devel \
       zlib-static \
       glib2-devel \
-      fftw-static \
-      fftw-devel \
       fontconfig-devel \
       zlib-static \
       java-21-openjdk-headless \

docker/rocky9/Dockerfile

@@ -59,8 +59,6 @@ RUN dnf -y update && \
       zlib-devel \
       zlib-static \
       glib2-devel \
-      fftw-static \
-      fftw-devel \
       zlib-static \
       fontconfig-devel \
       mesa-dri-drivers \

docker/ubuntu2204/Dockerfile

@@ -72,7 +72,6 @@ RUN set -eux; \
       zlib1g-dev \
       libglib2.0-dev \
       libfontconfig1-dev \
-      libfftw3-dev \
       libdrm-dev \
       mesa-utils \
       libassimp-dev \

docker/ubuntu2404/Dockerfile

@@ -72,7 +72,6 @@ RUN set -eux; \
       zlib1g-dev \
       libglib2.0-dev \
       libfontconfig1-dev \
-      libfftw3-dev \
       libdrm-dev \
       libglvnd-dev \
       libassimp-dev \