Remove GD_EMAC target from build configuration

Removed GD_EMAC target from CMakeLists.txt.

Author: JohnK1987

connectivity/drivers/emac/CMakeLists.txt

@@ -20,8 +20,6 @@ elseif("Cypress" IN_LIST MBED_TARGET_LABELS)
     add_subdirectory(TARGET_Cypress)
 elseif("Freescale_EMAC" IN_LIST MBED_TARGET_LABELS)
     add_subdirectory(TARGET_Freescale_EMAC)
-elseif("GD_EMAC" IN_LIST MBED_TARGET_LABELS)
-    add_subdirectory(TARGET_GD_EMAC)
 elseif("NUVOTON_EMAC" IN_LIST MBED_TARGET_LABELS)
     add_subdirectory(TARGET_NUVOTON_EMAC)
 elseif("NXP_EMAC" IN_LIST MBED_TARGET_LABELS)