Revert "Bump Modelica language version to 3.5"

This reverts commit c015bfc.

Bumping language version is now made the separate PR modelica#4208.

Modelica/package.mo

@@ -2444,7 +2444,7 @@ Short Overview:
 </p>
 <ul>
 <li>About <a href=\"modelica://Modelica/Resources/Documentation/Version-4.0.0/ResolvedGitHubIssues.html\">649 issues (including 432 pull requests)</a> have been addressed for this release.</li>
-<li>This version is based on the recent Modelica language standard version 3.5.</li>
+<li>This version is based on the recent Modelica language standard version 3.4.</li>
 <li>The library version (i.e., \"4.0.0\") follows semantic versioning using the convention <code>MAJOR.MINOR.BUGFIX</code>
 (see <a href=\"modelica://Modelica.UsersGuide.ReleaseNotes.VersionManagement\">Version Management</a> for details)
  and was decoupled from the version of the utilized version of the Modelica language standard.</li>
@@ -9071,7 +9071,7 @@ This version of the Modelica Standard Library consists of
 </ul>
 <p>
 that are directly usable (= number of public, non-partial, non-internal and non-obsolete classes). It is fully compliant
-to <a href=\"https://specification.modelica.org/maint/3.5/MLS.html\">Modelica Specification version 3.5</a>
+to <a href=\"https://modelica.org/documents/ModelicaSpec34.pdf\">Modelica Specification version 3.4</a>
 and it has been tested with Modelica tools from different vendors.
 </p>