Export: Remove DS-5

### Description

The DS-5 exporter does not work. It exports projects which I'm 100% sure
don't build. I have been looking over supporting it for about 6 months
now and I have convinced myself that I don't think it's worth the
trouble. Shout now if you need this exporter.

### Pull request type

    [ ] Fix
    [ ] Refactor
    [ ] Target update
    [x] Functionality change
    [ ] Docs update
    [ ] Test update
    [ ] Breaking change

Author: theotherjimmy

tools/export/__init__.py

@@ -29,7 +29,7 @@
 from ..config import ALLOWED_FEATURES
 from ..build_api import prepare_toolchain
 from ..targets import TARGET_NAMES
-from . import (lpcxpresso, ds5_5, iar, makefile, embitz, coide, kds, simplicity,
+from . import (lpcxpresso, iar, makefile, embitz, coide, kds, simplicity,
                atmelstudio, mcuxpresso, sw4stm32, e2studio, zip, cmsis, uvision,
                cdt, vscode, gnuarmeclipse, qtcreator, cmake, nb, cces, codeblocks)
 
@@ -40,7 +40,6 @@
     u'make_armc5': makefile.Armc5,
     u'make_armc6': makefile.Armc6,
     u'make_iar': makefile.IAR,
-    u'ds5_5': ds5_5.DS5_5,
     u'iar': iar.IAR,
     u'embitz' : embitz.EmBitz,
     u'sw4stm32'    : sw4stm32.Sw4STM32,