all: remove Linux 2.4 vs 2.6 detection

Linux 2.4 is dead.
(The libthread code hasn't worked for Linux 2.4 for a long time.)

INSTALL

@@ -66,23 +66,6 @@ DragonFly|*BSD)
 esac
 
 (
-if [ `uname` = Linux ]; then
-	# On Linux, we use the kernel version to decide whether
-	# to use pthreads or not.  On 2.6 versions that aren't
-	# linking with NPTL by default, pretend to be an older kernel.
-	echo "* Running on Linux: checking for NPTL..."
-	gcc lib/linux-isnptl.c -lpthread
-	if ./a.out >/dev/null
-	then	
-		echo "	NPTL found."
-		echo "SYSVERSION=2.6.x" >>$PLAN9/config
-	else
-		echo "	NPTL not found."
-		echo "SYSVERSION=2.4.x" >>$PLAN9/config
-	fi
-	rm -f ./a.out
-fi
-
 if [ `uname` = SunOS ]; then
 	# On Solaris x86, uname -p cannot be trusted.
 	echo "* Running on Solaris: checking architecture..."
@@ -168,7 +151,7 @@ if $dobuild; then
 		echo "* Error: mk failed to build."
 		exit 1
 	fi
-	
+
 	echo "* Building everything (be patient)..."
 	mk clean
 	mk libs-nuke
@@ -216,13 +199,13 @@ if $doinstall; then
 			mk man
 		)
 	fi
-	
+
 	if [ -x LOCAL.INSTALL ]; then
 		echo "* Running local modifications..."
 		echo cd `pwd`';' ./LOCAL.INSTALL
 		./LOCAL.INSTALL
 	fi
-	
+
 	echo "* Done. "
 	echo "	"
 	echo "* Add these to your profile environment."