Remove unused attribute from __table macros; the tables are no longer

static since otherwise gcc4 optimises them away completely.  Also, it
really *is* an error if the table start and end are unused, so they
certainly shouldn't be marked with attribute unused.

src/include/gpxe/tables.h

  *
  */
 #define __table(table,idx) \
-	__attribute__ (( unused, __table_section(table,idx) ))
+	__attribute__ (( __table_section(table,idx) ))
 
 /**
  * Linker table start marker.
  *
  */
 #define __table_start(table) \
-	__attribute__ (( unused, __table_section_start(table) ))
+	__attribute__ (( __table_section_start(table) ))
 
 /**
  * Linker table end marker.
  *
  */
 #define __table_end(table) \
-	__attribute__ (( unused, __table_section_end(table) ))
+	__attribute__ (( __table_section_end(table) ))
 
 #endif /* _GPXE_TABLES_H */