Remove virtual/webruntime RPROVIDES

At this point it is not really the case that WAM can be switched
out for another web runtime, so just remove the virtual/webruntime
RPROVIDES rather than rework it.

Bug-AGL: SPEC-5067

Change-Id: I0b55f483352c93e50e36d25d6237abe3598552b4
Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl-demo/+/29624
Tested-by: Jenkins Job builder account
ci-image-build: Jenkins Job builder account
ci-image-boot-test: Jenkins Job builder account
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>