Remove most includes of psymtab.h

I found that most spots including psymtab.h do not need it.  This
patch removes these includes, and also one unnecessary include of
psympriv.h.

gdb/coffread.c

@@ -40,7 +40,6 @@
 
 #include "coff-pe-read.h"
 
-#include "psymtab.h"
 #include "build-id.h"
 
 /* The objfile we are currently reading.  */

gdb/elfread.c

@@ -30,7 +30,6 @@
 #include "objfiles.h"
 #include "stabsread.h"
 #include "demangle.h"
-#include "psympriv.h"
 #include "filenames.h"
 #include "probe.h"
 #include "arch-utils.h"

gdb/mi/mi-cmd-file.c

@@ -25,7 +25,6 @@
 #include "symtab.h"
 #include "source.h"
 #include "objfiles.h"
-#include "psymtab.h"
 #include "solib.h"
 #include "solist.h"
 #include "gdbsupport/gdb_regex.h"

gdb/mipsread.c

@@ -39,8 +39,6 @@
 #include "elf/internal.h"
 #include "elf/mips.h"
 
-#include "psymtab.h"
-
 static void
 read_alphacoff_dynamic_symtab (minimal_symbol_reader &,
 			       struct objfile *objfile);

gdb/objfiles.c

@@ -47,7 +47,6 @@
 #include "exec.h"
 #include "observable.h"
 #include "complaints.h"
-#include "psymtab.h"
 #include "solist.h"
 #include "gdb_bfd.h"
 #include "btrace.h"

gdb/objfiles.h

@@ -27,7 +27,6 @@
 #include "progspace.h"
 #include "registry.h"
 #include "gdb_bfd.h"
-#include "psymtab.h"
 #include <atomic>
 #include <bitset>
 #include <vector>

gdb/rust-lang.c

@@ -29,7 +29,6 @@
 #include "gdbarch.h"
 #include "infcall.h"
 #include "objfiles.h"
-#include "psymtab.h"
 #include "rust-lang.h"
 #include "typeprint.h"
 #include "valprint.h"

gdb/stabsread.h

@@ -168,6 +168,8 @@ extern void end_stabs (void);
 
 extern void finish_global_stabs (struct objfile *objfile);
 
+class psymtab_storage;
+
 /* Functions exported by dbxread.c.  These are not in stabsread.c because
    they are only used by some stabs readers.  */