[gparted] Stop using removed btrfsctl (!26)

[Curtis Gedak <gedakc src gnome org>]

commit f697d1e7ceb76913edbc7126cb9e60b5797ce290
Author: Mike Fleetwood <mike fleetwood googlemail com>
Date:   Mon Mar 11 21:36:42 2019 +0000

    Stop using removed btrfsctl (!26)
    
    That commit [1] also removed btrfsctl from btrfs-progs 3.12 so also stop
    using it as a fallback.
    
    [1] 
https://git.kernel.org/pub/scm/linux/kernel/git/kdave/btrfs-progs.git/commit/?id=f243fcd1b2aa55ffadfbcc032c66dedbee56e79e
        Removing btrfsctl, btrfs-vol, btrfs-show
    
    Closes !26 - Remove support for btrfs-progs < 3.12

 src/btrfs.cc | 32 ++++----------------------------
 1 file changed, 4 insertions(+), 28 deletions(-)
---
diff --git a/src/btrfs.cc b/src/btrfs.cc
index fb4a1be0..5e679ec3 100644
--- a/src/btrfs.cc
+++ b/src/btrfs.cc
@@ -29,8 +29,6 @@
 namespace GParted
 {
 
-bool btrfs_found = false ;
-
 // Cache of required btrfs file system device information by device
 // E.g. For a single device btrfs on /dev/sda2 and a three device btrfs
 //      on /dev/sd[bcd]1 the cache would be as follows.  (Note that
@@ -56,8 +54,7 @@ FS btrfs::get_filesystem_support()
        if ( ! Glib::find_program_in_path( "btrfsck" ) .empty() )
                fs.check = FS::EXTERNAL;
 
-       btrfs_found = ( ! Glib::find_program_in_path( "btrfs" ) .empty() ) ;
-       if ( btrfs_found )
+       if (! Glib::find_program_in_path("btrfs").empty())
        {
                //Use newer btrfs multi-tool control command.  No need
                //  to test for filesystem show and filesystem resize
@@ -84,24 +81,6 @@ FS btrfs::get_filesystem_support()
                if ( ! Utils::execute_command( "btrfs filesystem label --help", output, error, true ) )
                        fs .write_label = FS::EXTERNAL;
        }
-       else
-       {
-               // Fall back to using btrfsctl which was depreciated October 2011.
-
-               //Resizing of btrfs requires btrfsctl, mount, umount
-               //  and kernel support
-               if (    ! Glib::find_program_in_path( "btrfsctl" ) .empty()
-                    && ! Glib::find_program_in_path( "mount" ) .empty()
-                    && ! Glib::find_program_in_path( "umount" ) .empty()
-                    && fs .check
-                    && Utils::kernel_supports_fs( "btrfs" )
-                  )
-               {
-                       fs .grow = FS::EXTERNAL ;
-                       if ( fs .read ) //needed to determine a minimum file system size.
-                               fs .shrink = FS::EXTERNAL ;
-               }
-       }
 
        if ( ! Glib::find_program_in_path( "btrfstune" ).empty() )
        {
@@ -325,12 +304,9 @@ bool btrfs::resize( const Partition & partition_new, OperationDetail & operation
                                        partition_new .get_sector_length(), partition_new .sector_size, 
UNIT_KIB ) ) ) + "K" ;
                else
                        size = "max" ;
-               Glib::ustring cmd ;
-               if ( btrfs_found )
-                       cmd = "btrfs filesystem resize " + devid_str + ":" + size + " " + Glib::shell_quote( 
mount_point );
-               else
-                       cmd = "btrfsctl -r " + devid_str + ":" + size + " " + Glib::shell_quote( mount_point 
);
-               success &= ! execute_command(cmd, operationdetail, EXEC_CHECK_STATUS);
+               success &= ! execute_command("btrfs filesystem resize " + devid_str + ":" + size +
+                                            " " + Glib::shell_quote(mount_point),
+                                             operationdetail, EXEC_CHECK_STATUS);
 
                if ( ! partition_new .busy )
                        success &= ! execute_command( "umount -v " + Glib::shell_quote( mount_point ),