[build] Fix lexer build issue on gcc-10.

Compiling under GCC 10 leads to build errors about duplicate symbol
"yylloc". Remove the item causing the problem, which has also been
done in upstream versions of Linux.

Change-Id: Ic80fa141314312555b1cdf466ec207fddf27aa67

scripts/dtc/dtc-lexer.l

diff --git a/scripts/dtc/dtc-lexer.l b/scripts/dtc/dtc-lexer.l
index 615b7ec..d3694d6 100644
--- a/scripts/dtc/dtc-lexer.l
+++ b/scripts/dtc/dtc-lexer.l
@@ -38,7 +38,6 @@
 #include "srcpos.h"
 #include "dtc-parser.tab.h"
 
-YYLTYPE yylloc;
 extern bool treesource_error;
 
 /* CAUTION: this will stop working if we ever use yyless() or yyunput() */