Delete readline/ (the vendored GNU readline 4.3, ~104 files / 2 MB) now that
configure requires the system readline (Patch 1) and the Makefiles no longer
wire the bundled build (Patch 2). Sweep the remaining references:
* commands/Makefile.in: drop the `module: ${MAGICDIR}/readline/readline` rule
and the readline-create-symlinks delegation (bundled-only; commands now uses
the default `module: libcommands.o`).
* commands/CmdFI.c, textio/txMain.c, textio/txInput.c: the readline includes
had a `#ifdef HAVE_READLINE <system> #else "readline/readline/*.h" (bundled)`
split. HAVE_READLINE/NEED_READLINE are used nowhere else and USE_READLINE now
always implies the system library, so collapse to the plain
`#include <readline/readline.h>` / `<history.h>`.
* CI: main.yml's non-Tcl job installs libreadline-dev (was relying on bundled);
canary-matrix drops the now-invalid no_tk_tcl_brl / --enable-readline-bundled
variant.
* .gitignore: drop the "readline/ intentionally not converted" note.
Verified: Tcl -j12 builds+installs 375 files (commands builds, no readline-dir
references); --without-tcl --disable-readline -j12 builds (x2); --without-tcl with
no readline dev package still errors with the guidance message.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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