Use upper case for more metasyntactic variables in gdb

Use upper case for more metasyntactic variables in gdb

I noticed a few places where a Usage line in gdb did not use upper
case for metasyntactic variables.  This patch fixes all the instances
I found.

Tested on x86-64 Fedora 28.

gdb/ChangeLog
2019-01-04  Tom Tromey  <tom@tromey.com>

	* compile/compile.c (_initialize_compile): Use upper case for
	metasyntactic variables.
	* symmisc.c (_initialize_symmisc): Use upper case for
	metasyntactic variables.
	* psymtab.c (_initialize_psymtab): Use upper case for
	metasyntactic variables.
	* demangle.c (demangle_command): Use upper case for metasyntactic
	variables.
	(_initialize_demangler): Likewise.
	* ax-gdb.c (_initialize_ax_gdb): Use upper case for metasyntactic
	variables.