Centralise configuration of Shellbox /bin/sh location

Use $wgShellboxShell, introduced for this purpose in
If41a2baada2e4e2462518c1f437af458feb29632.

Change-Id: Ic35598f26a868624a8b2e37ab064a6c0c27e392f

extension.json

@@ -9,7 +9,7 @@
 	"license-name": "GPL-2.0-or-later",
 	"type": "media",
 	"requires": {
-		"MediaWiki": ">= 1.41"
+		"MediaWiki": ">= 1.42"
 	},
 	"config": {
 		"PdfOutputExtension": {
@@ -32,9 +32,6 @@
 		},
 		"PdfInfo": {
 			"value": "/usr/bin/pdfinfo"
-		},
-		"PdfHandlerShell": {
-			"value": "/bin/sh"
 		}
 	},
 	"MessagesDirs": {

includes/PdfImage.php

@@ -104,7 +104,7 @@ class PdfImage {
 	 * @return array
 	 */
 	public function retrieveMetaData(): array {
-		global $wgPdfInfo, $wgPdftoText, $wgPdfHandlerShell;
+		global $wgPdfInfo, $wgPdftoText, $wgShellboxShell;
 
 		$command = MediaWikiServices::getInstance()->getShellCommandFactory()
 			->createBoxed( 'pdfhandler' )
@@ -113,7 +113,7 @@ class PdfImage {
 			->routeName( 'pdfhandler-metadata' );
 
 		$result = $command
-			->params( $wgPdfHandlerShell, 'scripts/retrieveMetaData.sh' )
+			->params( $wgShellboxShell, 'scripts/retrieveMetaData.sh' )
 			->inputFileFromFile(
 				'scripts/retrieveMetaData.sh',
 				__DIR__ . '/../scripts/retrieveMetaData.sh' )