[gdb/testsuite, tclint] Drop lreverse

When running tclint with lib/future.exp, I get:
...
$ tclint lib/future.exp
$exp:756:5: redefinition of built-in command 'lreverse' [redefined-builtin]
...

The code was added to handle pre-7.5 tcl versions without lreverse.

Since we now require Tcl 8.6.2 (as per PR testsuite/33205), drop this.

Tested by rerunning tclint.

Approved-By: Simon Marchi <[email protected]>

PR testsuite/33403
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33403

Author: vries

gdb/testsuite/lib/future.exp

@@ -749,19 +749,6 @@ if { [array size use_gdb_compile] != 0 } {
     rename gdb_default_target_compile ""
 }
 
-
-# Provide 'lreverse' missing in Tcl before 7.5.
-
-if {[info procs lreverse] == ""} {
-    proc lreverse { arg } {
-	set retval {}
-	while { [llength $retval] < [llength $arg] } {
-	    lappend retval [lindex $arg end-[llength $retval]]
-	}
-	return $retval
-    }
-}
-
 # Various ccache versions provide incorrect debug info such as ignoring
 # different current directory, breaking GDB testsuite.
 set env(CCACHE_DISABLE) 1