Fix warnings caused by unnecessary `mut` qualifiers (#735)

components/imageproc/src/lib.rs

@@ -300,7 +300,7 @@ impl ImageOp {
 
         match self.format {
             Format::Png => {
-                let mut enc = PNGEncoder::new(&mut f);
+                let enc = PNGEncoder::new(&mut f);
                 enc.encode(&img.raw_pixels(), img_w, img_h, img.color())?;
             }
             Format::Jpeg(q) => {

components/library/src/library.rs

@@ -139,7 +139,7 @@ impl Library {
                 let parent_is_transparent;
                 // We need to get a reference to a section later so keep the scope of borrowing small
                 {
-                    let mut section = self.sections.get_mut(*section_key).unwrap();
+                    let section = self.sections.get_mut(*section_key).unwrap();
                     section.pages.push(key);
                     parent_is_transparent = section.meta.transparent;
                 }

components/utils/src/de.rs

@@ -40,7 +40,7 @@ pub fn fix_toml_dates(table: Map<String, Value>) -> Value {
 
     for (key, value) in table {
         match value {
-            Value::Object(mut o) => {
+            Value::Object(o) => {
                 new.insert(key, convert_toml_date(o));
             }
             _ => {