cmd/5l, cmd/6l, cmd/8l: remove declaration on non-existent variables.

R=golang-dev, minux.ma
CC=golang-dev
https://golang.org/cl/7985043

src/cmd/5l/l.h

@@ -299,7 +299,6 @@ EXTERN	Auto*	curhist;
 EXTERN	Prog*	curp;
 EXTERN	Sym*	cursym;
 EXTERN	Sym*	datap;
-EXTERN	int32 	elfdatsize;
 EXTERN	int	debug[128];
 EXTERN	Sym*	etextp;
 EXTERN	char*	noname;

src/cmd/6l/l.h

@@ -336,7 +336,6 @@ EXTERN	Auto*	curhist;
 EXTERN	Prog*	curp;
 EXTERN	Sym*	cursym;
 EXTERN	Sym*	datap;
-EXTERN	vlong	elfdatsize;
 EXTERN	int	debug[128];
 EXTERN	char	literal[32];
 EXTERN	Sym*	textp;

src/cmd/8l/l.h

@@ -286,14 +286,12 @@ EXTERN	int32	INITTEXT;
 EXTERN	int32	INITDAT;
 EXTERN	char*	INITENTRY;		/* entry point */
 EXTERN	char*	LIBINITENTRY;		/* shared library entry point */
-EXTERN	int32	casepc;
 EXTERN	char*	pcstr;
 EXTERN	Auto*	curauto;
 EXTERN	Auto*	curhist;
 EXTERN	Prog*	curp;
 EXTERN	Sym*	cursym;
 EXTERN	Sym*	datap;
-EXTERN	int32	elfdatsize;
 EXTERN	int	debug[128];
 EXTERN	char	literal[32];
 EXTERN	Sym*	etextp;
@@ -319,7 +317,6 @@ EXTERN	int	dtype;
 EXTERN	int	tlsoffset;
 EXTERN	Sym*	adrgotype;	// type symbol on last Adr read
 EXTERN	Sym*	fromgotype;	// type symbol on last p->from read
-EXTERN	int	elftextsh;
 
 extern	Optab	optab[];
 extern	char*	anames[];