ir-core: Fix the delete logic

Instead of removing an entry, the logic were doing both a deletion and
a key addition, as shown by the log:

[11517.323314] ir_getkeycode: unknown key for scancode 0x0050
[11517.326529] ir_do_setkeycode: #80: Deleting scan 0x0050
[11517.326529] ir_do_setkeycode: #80: New scan 0x0050 with key 0x0000
[11517.340598] ir_getkeycode: unknown key for scancode 0x0051
[11517.343811] ir_do_setkeycode: #81: Deleting scan 0x0051
[11517.343811] ir_do_setkeycode: #81: New scan 0x0051 with key 0x0000
[11517.357889] ir_getkeycode: unknown key for scancode 0x0052
[11517.361104] ir_do_setkeycode: #82: Deleting scan 0x0052
[11517.361104] ir_do_setkeycode: #82: New scan 0x0052 with key 0x0000
[11517.375453] ir_getkeycode: unknown key for scancode 0x0053
[11517.378474] ir_do_setkeycode: #83: Deleting scan 0x0053
[11517.378474] ir_do_setkeycode: #83: New scan 0x0053 with key 0x0000

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>