rm eigen from docs

hugo/content/installation/building/unix/third-party.md

@@ -12,7 +12,6 @@ Required software:
    * `clang >= 7`
 * `cmake >= 3.14`
 * `gsl >= 1.15` (GNU scientific library)
-* `libeigen >=3`
 * `fftw3 >= 3.3.1`
 * `libtiff >=4.0.2`
 * `libcerf >=1.14` (complex error function, maintained by us)
@@ -43,11 +42,10 @@ very similar.
 Install required packages:
 ```
 $ sudo apt-get install build-essential git cmake \
-  libgsl-dev libeigen3-dev libfftw3-dev \
+  libgsl-dev libfftw3-dev libtiff5-dev \
   python3 python3-dev python3-numpy python3-matplotlib \
-  libtiff5-dev libboost-dev \
+  libboost-dev libboost-iostreams-dev \
   libboost-program-options-dev libboost-regex-dev \
-  libboost-iostreams-dev \
   qt5-default libqt5designercomponents5 qttools5-dev \
   libqt5svg5-dev libqt5opengl5-dev
 ```
@@ -55,7 +53,7 @@ $ sudo apt-get install build-essential git cmake \
 ### OpenSuse
 Install required packages:
 ```
-$ sudo zypper install gcc-c++ git-core cmake gsl-devel libeigen \
+$ sudo zypper install gcc-c++ git-core cmake gsl-devel \
   libboost_*-devel fftw3-devel python3-devel python3-numpy-devel \
   python3-matplotlib libtiff-devel \
   libqt5-qtbase-devel libqt5-qttools-devel libqt5-qtsvg-devel
@@ -71,7 +69,7 @@ Install extra packages:
 
 Install BornAgain dependencies:
     <pre><code>$ sudo yum -y install make cmake3 gcc-c++
-$ sudo yum -y install fftw-devel boost-devel gsl-devel eigen3-devel libtiff-devel
+$ sudo yum -y install fftw-devel boost-devel gsl-devel libtiff-devel
 $ sudo yum -y install python3-devel numpy
 $ sudo yum -y install qt5-qtbase-devel qt5-qttools-devel qt5-qtsvg-devel</code></pre>
 
@@ -111,7 +109,7 @@ Install Homebrew as explained <a href=https://brew.sh/>here</a> and
 then install all BornAgain dependencies by running the following
 commands:
 ```
-brew install git cmake fftw gsl python boost libtiff eigen qt5
+brew install git cmake fftw gsl python boost libtiff qt5
 pip3 install matplotlib numpy
 ```