[PATCH] Update the 'g' packet documentation

[Tom Tromey <tromey@adacore.com>]

The 'g' packet documentation references a macro that no longer exists,
and it also claims that the 'x' response for an unavailable register
is limited to trace frames.  This patch updates the documentation to
reflect what I think is currently correct.
---
 gdb/doc/gdb.texinfo | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 9c0018ea5c1..80584241870 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -41318,11 +41318,12 @@ Reply:
 Each byte of register data is described by two hex digits.  The bytes
 with the register are transmitted in target byte order.  The size of
 each register and their position within the @samp{g} packet are
-determined by the @value{GDBN} internal gdbarch functions
-@code{DEPRECATED_REGISTER_RAW_SIZE} and @code{gdbarch_register_name}.
+determined by the target description (@pxref{Target Descriptions}); in
+the absence of a target description, this is done using code internal
+to @value{GDBN}; typically this is some customary register layout for
+the architecture in question.
 
-When reading registers from a trace frame (@pxref{Analyze Collected
-Data,,Using the Collected Data}), the stub may also return a string of
+When reading registers, the stub may also return a string of
 literal @samp{x}'s in place of the register data digits, to indicate
 that the corresponding register has not been collected, thus its value
 is unavailable.  For example, for an architecture with 4 registers of
-- 
2.38.1