I was personally able to remove permissions by creating a ManifestRequirementsOverride.txt in [ProjectName]/Build/Android/ (same folder as your keystore)
The content looks like this in my case:
<uses-sdk android:minSdkVersion="26"/>
<uses-feature android:glEsVersion="0x00030002" android:required="true" />
<uses-permission android:name="android.permission.RECORD_AUDIO" tools:node="remove"/>