tests: net: http_server: Remove harness requirement

The HTTP server tests are self-contained, they do not require network
environment to execute, hence should not specify "harness: net".

The consequence of specifying the harness was that HTTP server tests in
the CI were only built, and not executed, which doesn't make much sense.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>

tests/net/lib/http_server/core/testcase.yaml

@@ -1,5 +1,4 @@
 common:
-  harness: net
   min_ram: 80
   tags:
     - http

tests/net/lib/http_server/crime/testcase.yaml

@@ -1,5 +1,4 @@
 common:
-  harness: net
   min_ram: 60
   tags:
     - http

tests/net/lib/http_server/hpack/testcase.yaml

@@ -1,5 +1,4 @@
 common:
-  harness: net
   depends_on: netif
   min_ram: 60
   tags:

tests/net/lib/http_server/tls/testcase.yaml

@@ -1,5 +1,4 @@
 common:
-  harness: net
   min_ram: 192
   tags:
     - http