add new Literal API for pure literal expressions:

Design compile time api hs_compile_lit() and hs_compile_lit_multi()
to handle pure literal pattern sets. Corresponding option --literal-on
is added for hyperscan testing suites. Extended parameters and part of
flags are not supported for this api.

src/scratch.h

@@ -211,7 +211,6 @@ struct ALIGN_CL_DIRECTIVE hs_scratch {
     u64a *fdr_conf; /**< FDR confirm value */
     u8 fdr_conf_offset; /**< offset where FDR/Teddy front end matches
                          * in buffer */
-    u8 pure; /**< indicator of pure-literal or cutting-literal */
 };
 
 /* array of fatbit ptr; TODO: why not an array of fatbits? */