Remove File::toml and File::yaml

The added convenience is minimal over `new`, so I'd rather have a
smaller API and less code with `#[cfg]`.

src/file.rs

@@ -35,6 +35,7 @@ pub struct File {
 }
 
 impl File {
+    /// Creates an optional file source.
     pub fn new(path: impl Into<PathBuf>, format: FileFormat) -> Self {
         Self {
             path: path.into(),
@@ -43,16 +44,6 @@ impl File {
         }
     }
 
-    #[cfg(feature = "toml")]
-    pub fn toml(path: impl Into<PathBuf>) -> Self {
-        Self::new(path, FileFormat::Toml)
-    }
-
-    #[cfg(feature = "yaml")]
-    pub fn yaml(path: impl Into<PathBuf>) -> Self {
-        Self::new(path, FileFormat::Yaml)
-    }
-
     /// Marks this file as required, meaning that `<File as Source<_>>::load`
     /// will return an error if the file does not exist. Otherwise, an empty
     /// layer (all values are `None`) is returned.