Return deprecation errors for removed functionality.

[mondalaci]

/home/laci/projects/firmware/right/src/macros/commands.c: In function 'processCommand':
/home/laci/projects/firmware/right/src/macros/commands.c:2134:24: warning: implicit declaration of function 'processSetRegCommand'; did you mean 'processExecCommand'? [-Wimplicit-function-declaration]
 2134 |                 return processSetRegCommand(ctx);
      |                        ^~~~~~~~~~~~~~~~~~~~
      |                        processExecCommand
    CC    core.c
    CC    debug_commands.c
    CC    keyid_parser.c
    CC    scancode_commands.c
    CC    set_command.c
    CC    shortcut_parser.c
    CC    status_buffer.c
    CC    string_reader.c
    CC    vars.c
/home/laci/projects/firmware/right/src/macros/vars.c: In function 'consumeValue':
/home/laci/projects/firmware/right/src/macros/vars.c:343:135: error: 'a' undeclared (first use in this function)
  343 |             Macros_ReportError("Registers were removed. Please, replace them with named variables. E.g., `setVar foo 1` and `$foo`.", a, a);
      |                                                                                                                                       ^
/home/laci/projects/firmware/right/src/macros/vars.c:343:135: note: each undeclared identifier is reported only once for each function it appears in
make: *** [../../scripts/Makedefs.mk:220: build_make//home/laci/projects/firmware/right/src/macros/vars.o] Error 1

[kareltucek]

Oops, should be fixed!