REG-TESTS: cache: Remove T-E header for 304-Not-Modified responses

REG-TESTS: cache: Remove T-E header for 304-Not-Modified responses

VTEST does not properly handle 304-Not-Modified responses. If a
Transfer-Encoding header (and probably a Content-Lenght header too), it
waits for a body. Waiting for a fix, the Transfer-Encoding encoding of
cached responses in 2 VTEST scripts are removed.

Note it is now an issue because of a fix in the H1 multiplexer :

  * 226082d13a "BUG/MINOR: mux-h1: Do not send a last null chunk on body-less answers"

This patch must be backported with the above commit.