gdb, record: rephrase the 'not recording' error message

When trying to use one of the record commands without having enabled
recording first, GDB gives the error message:

    (gdb) record function-call-history
    No record target is currently active.
    Use one of the "target record-<TAB><TAB>" commands first.

In the record help, however, we say:

    (gdb) help record
    record, rec
    Start recording.

    List of record subcommands:

    record btrace, record b -- Start branch trace recording.
    record delete, record del, record d -- Delete the rest of execution log and start recording it anew.
    record full -- Start full execution recording.
    record function-call-history -- Prints the execution history at function granularity.
    record goto -- Restore the program to its state at instruction number N.
    record instruction-history -- Print disassembled instructions stored in the execution log.
    record save -- Save the execution log to a file.
    record stop, record s -- Stop the record/replay target.

Change the above error message to

    (gdb) record function-call-history
    No recording is currently active.
    Use the "record full" or "record btrace" command first.

to align with the help text.

gdb/ChangeLog:
2020-12-03  Markus Metzger  <markus.t.metzger@intel.com>

	* record.c (require_record_target): Rephrase error message.
	(info_record_command): Likewise.

gdb/testsuite/ChangeLog:
2020-12-03  Markus Metzger  <markus.t.metzger@intel.com>

	* gdb.btrace/enable.exp: Update error message.
	* gdb.btrace/multi-inferior.exp: Likewise.
	* gdb.btrace/reconnect.exp: Likewise.
	* gdb.python/py-record-btrace.exp: Likewise.
	* gdb.python/py-record-full.exp: Likewise.