[core] Fix modernize-use-equals-default errors

As reported by clang-tidy-8.

platform/default/src/mbgl/storage/sqlite3.cpp

@@ -187,6 +187,7 @@ Statement::Statement(Database& db, const char* sql)
     : impl(std::make_unique<StatementImpl>(db.impl->db, sql)) {
 }
 
+// NOLINTNEXTLINE(modernize-use-equals-default)
 Statement::~Statement() {
 #ifndef NDEBUG
     // Crash if we're destructing this object while we know a Query object references this.

platform/default/src/mbgl/text/local_glyph_rasterizer.cpp

@@ -7,8 +7,7 @@ class LocalGlyphRasterizer::Impl {
 
 LocalGlyphRasterizer::LocalGlyphRasterizer(const optional<std::string>&) {}
 
-LocalGlyphRasterizer::~LocalGlyphRasterizer()
-{}
+LocalGlyphRasterizer::~LocalGlyphRasterizer() = default;
 
 bool LocalGlyphRasterizer::canRasterizeGlyph(const FontStack&, GlyphID) {
     return false;