remove header name buffer

remove header name buffer

The header name buffer and its max length handling has actually
been unused since the minilex parser was introduced.  We hold
parsing state in the lex-type parts and don't need to store or
worry about max length, since the parser will let us know as
soon as it can't be a match for the valid header names.

This strips it out reducing the per-connection allocation for
x86_64 with default configure from 224 to 160.

Signed-off-by: Andy Green <andy.green@linaro.org>