oracle-instantclient: drop PECL::oci8 hack

This wasn't about PECL::oci8 in first place, but DBD-Oracle.

In the current version of oracle-instantclient, a libclntsh.so is
shipped, so DBD-Oracle is happy.

pkgs/development/libraries/oracle-instantclient/default.nix

@@ -112,11 +112,7 @@ in stdenv.mkDerivation {
     ln -sfn $out/bin/sqlplus $out/bin/sqlplus64
   '';
 
-  postFixup = ''
-    # PECL::oci8 will not build without this
-    # this symlink only exists in dist zipfiles for some platforms
-    ln -sfn $out/lib/libclntsh${extLib}.12.1 $out/lib/libclntsh${extLib}
-  '' + optionalString stdenv.isDarwin ''
+  postFixup = optionalString stdenv.isDarwin ''
     for exe in "$out/bin/"* ; do
       if [ ! -L "$exe" ]; then
         install_name_tool -add_rpath "$lib/lib" "$exe"
@@ -124,7 +120,6 @@ in stdenv.mkDerivation {
     done
   '';
 
-
   meta = with stdenv.lib; {
     description = "Oracle instant client libraries and sqlplus CLI";
     longDescription = ''