examples/rssi_report: fix syntax error of Kconfig
Remove redundant " to fix below
apps/examples/rssi_report/Kconfig:7:warning: multi-line strings not supported
#
config EXAMPLES_RSSI_REPORT
- bool "Sample App for reporting RSSI to server""
+ bool "Sample App for reporting RSSI to server"
default n
---help---
Enable the network test API's
