doc: Simplify description of --with-lz4

LZ4 is used in much more areas of the system now than just WAL and table
data.  This commit simplifies the installation documentation of Windows
and *nix by removing any details of the areas extended when building
with LZ4.

Author: Jeevan Ladhe
Discussion: https://postgr.es/m/CANm22Cgny8AF76pitomXp603NagwKXbA4dyN2Fac4yHPebqdqg@mail.gmail.com

doc/src/sgml/install-windows.sgml

@@ -300,9 +300,8 @@ $ENV{MSBFLAGS}="/m";
     <varlistentry>
      <term><productname>LZ4</productname></term>
      <listitem><para>
-      Required for supporting <productname>LZ4</productname> compression
-      method for compressing table or WAL data. Binaries and source can be
-      downloaded from
+      Required for supporting <productname>LZ4</productname> compression.
+      Binaries and source can be downloaded from
       <ulink url="https://github.com/lz4/lz4/releases"></ulink>.
      </para></listitem>
     </varlistentry>

doc/src/sgml/installation.sgml

@@ -979,8 +979,6 @@ build-postgresql:
        <listitem>
         <para>
          Build with <productname>LZ4</productname> compression support.
-         This allows the use of <productname>LZ4</productname> for
-         compression of table and WAL data.
         </para>
        </listitem>
       </varlistentry>