doc: Clarify project naming

Clarify the project naming in the history section of the docs
to match the recent license preamble changes.

Backpatch to all supported versions.

Author: Dave Page <[email protected]>
Reviewed-by: Daniel Gustafsson <[email protected]>
Discussion: https://postgr.es/m/CA+OCxozLzK2+Jc14XZyWXSp6L9Ot+3efwXUE35FJG=fsbib2EA@mail.gmail.com
Backpatch-through: 13

Author: danielgustafsson

doc/src/sgml/history.sgml

@@ -203,11 +203,10 @@
   </para>
 
   <para>
-   Many people continue to refer to
-   <productname>PostgreSQL</productname> as <quote>Postgres</quote>
-   (now rarely in all capital letters) because of tradition or because
-   it is easier to pronounce.  This usage is widely accepted as a
-   nickname or alias.
+   <productname>Postgres</productname> is still considered an official
+   project name, both because of tradition and because people find it
+   easier to pronounce <productname>Postgres</productname> than
+   <productname>PostgreSQL</productname>.
   </para>
 
   <para>