Update Caravel to `mpw-5a`

Also remove `make pdk-nonnative`.

Makefile

diff --git a/Makefile b/Makefile
index b14cf0b..6de652c 100644
--- a/Makefile
+++ b/Makefile
@@ -24,11 +24,11 @@
 ifeq ($(CARAVEL_LITE),1) 
 	CARAVEL_NAME := caravel-lite
 	CARAVEL_REPO := https://github.com/efabless/caravel-lite 
-	CARAVEL_TAG := 'mpw-5'
+	CARAVEL_TAG := 'mpw-5a'
 else
 	CARAVEL_NAME := caravel
 	CARAVEL_REPO := https://github.com/efabless/caravel 
-	CARAVEL_TAG := 'mpw-5'
+	CARAVEL_TAG := 'mpw-5a'
 endif
 
 
@@ -115,11 +115,6 @@
 	docker run -e INPUT_DIRECTORY=$(INPUT_DIRECTORY) -e PDK_ROOT=$(PDK_ROOT) -v $(PRECHECK_ROOT):$(PRECHECK_ROOT) -v $(INPUT_DIRECTORY):$(INPUT_DIRECTORY) -v $(PDK_ROOT):$(PDK_ROOT) \
 	-u $(shell id -u $(USER)):$(shell id -g $(USER)) efabless/mpw_precheck:latest bash -c "cd $(PRECHECK_ROOT) ; python3 mpw_precheck.py --pdk_root $(PDK_ROOT) --input_directory $(INPUT_DIRECTORY)"
 
-# Install PDK using OL's Docker Image
-.PHONY: pdk-nonnative
-pdk-nonnative: skywater-pdk skywater-library skywater-timing open_pdks
-	docker run --rm -v $(PDK_ROOT):$(PDK_ROOT) -v $(CARAVEL_ROOT):$(CARAVEL_ROOT) -e CARAVEL_ROOT=$(CARAVEL_ROOT) -e PDK_ROOT=$(PDK_ROOT) -u $(shell id -u $(USER)):$(shell id -g $(USER)) efabless/openlane:2021.09.19_20.25.16 sh -c "cd $(CARAVEL_ROOT); make build-pdk; make gen-sources"
-
 # Clean 
 .PHONY: clean
 clean:

docs/source/index.rst

diff --git a/docs/source/index.rst b/docs/source/index.rst
index 77df3d5..43caa60 100644
--- a/docs/source/index.rst
+++ b/docs/source/index.rst
@@ -173,12 +173,8 @@
 Building the PDK 
 ================
 
-You have two options for building the pdk: 
-
-- Build the pdk natively. 
-
 Make sure you have `Magic VLSI Layout Tool <http://opencircuitdesign.com/magic/index.html>`__ installed on your machine before building the pdk. 
-The pdk build is tested with magic version ``8.3.209``. 
+The pdk build is tested with magic version ``8.3.265``. 
 
 .. code:: bash
 
@@ -191,19 +187,6 @@
 
     make pdk
 
-- Build the pdk using openlane's docker image which has magic installed. 
-
-.. code:: bash
-
-    # set PDK_ROOT to the path you wish to use for the pdk
-    export PDK_ROOT=<pdk-installation-path>
-
-    # you can optionally specify skywater-pdk and open-pdks commit used
-    # by setting and exporting SKYWATER_COMMIT and OPEN_PDKS_COMMIT
-    # if you do not set them, they default to the last verfied commits tested for this project
-
-    make pdk-nonnative
-
 Running Full Chip Simulation
 ============================