Remove finfo class existence checks

As of PHP >= 5.3.0 finfo class is available [1] and enabled by default [2]

[1] http://www.php.net/manual/en/class.finfo.php
[2] http://www.php.net/manual/en/fileinfo.installation.php

Removed all runtime checks but kept them in install/check to have an easy way to find the case where someone disabled the extension.

Issue #23639

core/file_api.php

@@ -972,18 +972,17 @@ function file_get_content( $p_file_id, $p_type = 'bug' ) {
 
 	# If finfo is available (always true for PHP >= 5.3.0) we can use it to determine the MIME type of files
 	$t_finfo_available = false;
-	if( class_exists( 'finfo' ) ) {
-		$t_info_file = config_get_global( 'fileinfo_magic_db_file' );
 
-		if( is_blank( $t_info_file ) ) {
-			$t_finfo = new finfo( FILEINFO_MIME );
-		} else {
-			$t_finfo = new finfo( FILEINFO_MIME, $t_info_file );
-		}
+	$t_info_file = config_get_global( 'fileinfo_magic_db_file' );
 
-		if( $t_finfo ) {
-			$t_finfo_available = true;
-		}
+	if( is_blank( $t_info_file ) ) {
+		$t_finfo = new finfo( FILEINFO_MIME );
+	} else {
+		$t_finfo = new finfo( FILEINFO_MIME, $t_info_file );
+	}
+
+	if( $t_finfo ) {
+		$t_finfo_available = true;
 	}
 
 	$t_content_type = $t_row['file_type'];

core/utility_api.php

@@ -301,18 +301,17 @@ function get_font_path() {
  * @return finfo
  */
 function finfo_get_if_available() {
-	if( class_exists( 'finfo' ) ) {
-		$t_info_file = config_get_global( 'fileinfo_magic_db_file' );
 
-		if( is_blank( $t_info_file ) ) {
-			$t_finfo = new finfo( FILEINFO_MIME );
-		} else {
-			$t_finfo = new finfo( FILEINFO_MIME, $t_info_file );
-		}
+	$t_info_file = config_get_global( 'fileinfo_magic_db_file' );
 
-		if( $t_finfo ) {
-			return $t_finfo;
-		}
+	if( is_blank( $t_info_file ) ) {
+		$t_finfo = new finfo( FILEINFO_MIME );
+	} else {
+		$t_finfo = new finfo( FILEINFO_MIME, $t_info_file );
+	}
+
+	if( $t_finfo ) {
+		return $t_finfo;
 	}
 
 	return null;