device-pine64-{pinephone,pinetab}: disable sysrq config

removed sysrq.conf, it's already disabled in linux-postmarketos-allwinner armv7 && aarch64:

Symbol: MAGIC_SYSRQ [=n]                                                                                                                                                                                                                                        
Type  : bool                                                                                                                                                                                                                                                    
Defined at lib/Kconfig.debug:480                                                                                                                                                                                                                                
  Prompt: Magic SysRq key                                                                                                                                                                                                                                       
  Depends on: !UML                                                                                                                                                                                                                                              
  Location:                                                                                                                                                                                                                                                     
    -> Kernel hacking                                                                                                                                                                                                                                           
(1)   -> Generic Kernel Debugging Instruments                                                                                                                                                                                                                   
Selected by [n]:                                                                                                                                                                                                                                                
  - KGDB_SERIAL_CONSOLE [=n] && KGDB [=n] && TTY [=y] && HW_CONSOLE [=y]