Remove some trailing whitespace in documentation files

doc/src/sgml/hash.sgml

@@ -49,7 +49,7 @@
   contrast, a hash index allows accessing the bucket pages directly,
   thereby potentially reducing index access time in larger tables. This
   reduction in "logical I/O" becomes even more pronounced on indexes/data
-  larger than shared_buffers/RAM. 
+  larger than shared_buffers/RAM.
  </para>
 
  <para>
@@ -89,7 +89,7 @@
   overflow page becomes empty, overflow pages can be recycled for reuse
   in other buckets, though we never return them to the operating system.
   There is currently no provision to shrink a hash index, other than by
-  rebuilding it with REINDEX.  
+  rebuilding it with REINDEX.
   There is no provision for reducing the number of buckets, either.
  </para>
 

doc/src/sgml/ref/alter_collation.sgml

@@ -144,7 +144,7 @@ HINT:  Rebuild all objects affected by this collation and run ALTER COLLATION pg
    <para>
     When using Windows for collations, version information is only available
     for collations defined with BCP 47 language tags such as
-    <literal>en-US</literal>. 
+    <literal>en-US</literal>.
    </para>
   </note>
   <para>

doc/src/sgml/ref/alter_table.sgml

@@ -881,7 +881,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
        <listitem>
         <para>
          Records the old values of the columns of the primary key, if any.
-         This is the default for non-system tables. 
+         This is the default for non-system tables.
         </para>
        </listitem>
       </varlistentry>

doc/src/sgml/ref/pg_checksums.sgml

@@ -47,7 +47,7 @@ PostgreSQL documentation
 
   <para>
    When verifying checksums, every file in the cluster is scanned. When
-   enabling checksums, each relation file block with a changed checksum is 
+   enabling checksums, each relation file block with a changed checksum is
    rewritten in-place.
    Disabling checksums only updates the file <filename>pg_control</filename>.
   </para>