doc: remove llvm-config search from configure documentation

As of 4dd29b6, we no longer attempt to locate any other llvm-config
variant than plain llvm-config in configure-based builds; update the
documentation accordingly. (For Meson-based builds, we still use Meson's
LLVMDependencyConfigTool [0], which runs through a set of possible
suffixes [1], so no need to update the documentation there.)

[0]: https://github.com/mesonbuild/meson/blob/7d28ff29396f9d7043204de8ddc52226b9903811/mesonbuild/dependencies/dev.py#L184
[1]: https://github.com/mesonbuild/meson/blob/7d28ff29396f9d7043204de8ddc52226b9903811/mesonbuild/environment.py#L183

Author: Ole Peder Brandtzæg <olebra@samfundet.no>
Discussion: https://www.postgresql.org/message-id/20240518224601.gtisttjerylukjr5%40samfundet.no

Author: petere

doc/src/sgml/installation.sgml

@@ -941,12 +941,10 @@ build-postgresql:
         <para>
          <command>llvm-config</command><indexterm><primary>llvm-config</primary></indexterm>
          will be used to find the required compilation options.
-         <command>llvm-config</command>, and then
-         <command>llvm-config-$major-$minor</command> for all supported
-         versions, will be searched for in your <envar>PATH</envar>.  If
-         that would not yield the desired program,
-         use <envar>LLVM_CONFIG</envar> to specify a path to the
-         correct <command>llvm-config</command>. For example
+         <command>llvm-config</command> will be searched for in your
+         <envar>PATH</envar>.  If that would not yield the desired program,
+         use <envar>LLVM_CONFIG</envar> to specify a path to the correct
+         <command>llvm-config</command>. For example
 <programlisting>
 ./configure ... --with-llvm LLVM_CONFIG='/path/to/llvm/bin/llvm-config'
 </programlisting>