libmounts: Remove two dead functions.

find_mounted_volume_by_device() and remount_read_only() have no active
users. And we don't have a code logic that requires these two functions.

Test: mmma bootable/recovery
Test: Code search shows no user.
Change-Id: Ib11c2ba93ee087ea020c1337eb06686a6165f894
diff --git a/mounts.cpp b/mounts.cpp
index fbcbac0..76fa657 100644
--- a/mounts.cpp
+++ b/mounts.cpp
@@ -62,13 +62,6 @@
     return true;
 }
 
-MountedVolume* find_mounted_volume_by_device(const char* device) {
-    for (size_t i = 0; i < g_mounts_state.size(); ++i) {
-        if (g_mounts_state[i]->device == device) return g_mounts_state[i];
-    }
-    return nullptr;
-}
-
 MountedVolume* find_mounted_volume_by_mount_point(const char* mount_point) {
     for (size_t i = 0; i < g_mounts_state.size(); ++i) {
         if (g_mounts_state[i]->mount_point == mount_point) return g_mounts_state[i];
@@ -87,13 +80,3 @@
   }
   return result;
 }
-
-int remount_read_only(MountedVolume* volume) {
-  int result = mount(volume->device.c_str(), volume->mount_point.c_str(),
-                     volume->filesystem.c_str(),
-                     MS_NOATIME | MS_NODEV | MS_NODIRATIME | MS_RDONLY | MS_REMOUNT, 0);
-  if (result == -1) {
-    PLOG(WARNING) << "Failed to remount read-only " << volume->mount_point;
-  }
-  return result;
-}
diff --git a/mounts.h b/mounts.h
index 1b76703..0de1ebd 100644
--- a/mounts.h
+++ b/mounts.h
@@ -21,12 +21,8 @@
 
 bool scan_mounted_volumes();
 
-MountedVolume* find_mounted_volume_by_device(const char* device);
-
 MountedVolume* find_mounted_volume_by_mount_point(const char* mount_point);
 
 int unmount_mounted_volume(MountedVolume* volume);
 
-int remount_read_only(MountedVolume* volume);
-
 #endif