microphone: remove extra newline and spaces

The extra line was causing newline chars and whitespaces to be added to translation strings

The following string for translation is currently extracted from source:

#: panels/microphone/cc-microphone-panel.ui:34
msgid ""
"Use of the microphone allows applications to record and listen to audio. "
"Disabling the microphone may cause some applications to not function "
"properly.\n"
"\n"
"Allow the applications below to use your microphone.\n"
"                    "
msgstr ""