LibCore: Remove unused API from DeprecatedFile

It looks like this migration it taking a while, so let's make sure noone
accidentally introduces new usages of this currently-unused API.

Userland/Libraries/LibCore/DeprecatedFile.cpp

@@ -143,11 +143,6 @@ bool DeprecatedFile::is_link() const
     return S_ISLNK(stat.st_mode);
 }
 
-bool DeprecatedFile::looks_like_shared_library() const
-{
-    return m_filename.ends_with(".so"sv) || m_filename.contains(".so."sv);
-}
-
 DeprecatedString DeprecatedFile::real_path_for(DeprecatedString const& filename)
 {
     if (filename.is_null())

Userland/Libraries/LibCore/DeprecatedFile.h

@@ -25,14 +25,12 @@ public:
     static ErrorOr<NonnullRefPtr<DeprecatedFile>> open(DeprecatedString filename, OpenMode, mode_t = 0644);
 
     DeprecatedString filename() const { return m_filename; }
-    void set_filename(const DeprecatedString filename) { m_filename = move(filename); }
 
     bool is_directory() const;
     bool is_device() const;
     bool is_block_device() const;
     bool is_char_device() const;
     bool is_link() const;
-    bool looks_like_shared_library() const;
 
     static DeprecatedString current_working_directory();
     static DeprecatedString absolute_path(DeprecatedString const& path);