browser-system: Use execv() directly instead of os_exec()

browser-system: Use execv() directly instead of os_exec()

This allows the URL to be passed as a single argument to the program
instead of getting split into multiple by os_exec(). This makes the
operation more robust for cases where the URL could have been received
from an external source and could potentially add extra arguments to the
command line.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>