Remove unused configure variable.

configure extracts TCL_SHLIB_LD_LIBS from tclConfig.sh, and puts the
value into Makefile.global, but then we never use it anywhere.  It
looks like I removed the only usage in cd75f94da, but didn't notice
that it was the only usage.  Might as well mop this up while we're
trying to get rid of unnecessary configure steps.

Discussion: https://postgr.es/m/2442359.1660835043@sss.pgh.pa.us

configure

@@ -634,7 +634,6 @@ DBTOEPUB
 FOP
 XSLTPROC
 XMLLINT
-TCL_SHLIB_LD_LIBS
 TCL_SHARED_BUILD
 TCL_LIB_SPEC
 TCL_LIBS
@@ -18818,7 +18817,7 @@ eval TCL_LIBS=\"$TCL_LIBS\"
 eval TCL_LIB_SPEC=\"$TCL_LIB_SPEC\"
 eval TCL_SHARED_BUILD=\"$TCL_SHARED_BUILD\"
 
-        if test "$TCL_SHARED_BUILD" != 1; then
+    if test "$TCL_SHARED_BUILD" != 1; then
       as_fn_error $? "cannot build PL/Tcl because Tcl is not a shared library
 Use --without-tcl to disable building PL/Tcl." "$LINENO" 5
     fi

configure.ac

@@ -2252,7 +2252,6 @@ if test "$with_tcl" = yes; then
     PGAC_PATH_TCLCONFIGSH([$with_tclconfig])
     PGAC_EVAL_TCLCONFIGSH([$TCL_CONFIG_SH],
                           [TCL_INCLUDE_SPEC,TCL_LIBS,TCL_LIB_SPEC,TCL_SHARED_BUILD])
-    AC_SUBST(TCL_SHLIB_LD_LIBS)dnl don't want to double-evaluate that one
     if test "$TCL_SHARED_BUILD" != 1; then
       AC_MSG_ERROR([cannot build PL/Tcl because Tcl is not a shared library
 Use --without-tcl to disable building PL/Tcl.])

src/Makefile.global.in

@@ -221,7 +221,6 @@ TCL_LIBS		= @TCL_LIBS@
 TCL_LIB_SPEC		= @TCL_LIB_SPEC@
 TCL_INCLUDE_SPEC	= @TCL_INCLUDE_SPEC@
 TCL_SHARED_BUILD	= @TCL_SHARED_BUILD@
-TCL_SHLIB_LD_LIBS	= @TCL_SHLIB_LD_LIBS@
 
 PTHREAD_CFLAGS		= @PTHREAD_CFLAGS@
 PTHREAD_LIBS		= @PTHREAD_LIBS@