Clean more legacy code (#3478)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/mbgl/gl/renderer_backend.cpp

@@ -8,6 +8,7 @@
 #include <mbgl/util/logging.hpp>
 
 #include <mbgl/shaders/gl/shader_group_gl.hpp>
+#include <mbgl/shaders/gl/legacy/programs.hpp>
 
 #include <cassert>
 
@@ -146,6 +147,10 @@ void RendererBackend::initShaders(gfx::ShaderRegistry& shaders, const ProgramPar
                   shaders::BuiltIn::SymbolIconShader,
                   shaders::BuiltIn::SymbolSDFShader,
                   shaders::BuiltIn::SymbolTextAndIconShader>(shaders, programParameters);
+
+    // Initialize legacy shader programs
+    Programs programs(programParameters);
+    programs.registerWith(shaders);
 }
 
 } // namespace gl