doc: Remove note about disk space from installation instructions

Seems quite outdated and no longer relevant.

Author: samay sharma <smilingsamay@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/CAJxrbywFPcgC4nP_v+HHPhaYSWX2JL8FZXY2aFOZxXxTkTJJPw@mail.gmail.com

doc/src/sgml/installation.sgml

@@ -342,17 +342,6 @@ su - postgres
    for a list) or at <ulink
    url="ftp://ftp.gnu.org/gnu/"></ulink>.
   </para>
-
-  <para>
-   Also check that you have sufficient disk space. You will need about
-   350 MB for the source tree during compilation and about 60 MB for
-   the installation directory. An empty database cluster takes about
-   40 MB; databases take about five times the amount of space that a
-   flat text file with the same data would take. If you are going to
-   run the regression tests you will temporarily need up to an extra
-   300 MB. Use the <command>df</command> command to check free disk
-   space.
-  </para>
  </sect1>
 
  <sect1 id="install-getsource">