Config option cleanups for Encoding API

* Remove Encoding API from low memory default config

* Wording fix for option description

config/config-options/DUK_USE_ENCODING_BUILTINS.yaml

@@ -10,4 +10,4 @@ description: >
 
   DUK_USE_BUFFEROBJECT_SUPPORT is recommended but not required: If it is
   disabled, TextEncoder will encode to a plain buffer instead of a Uint8Array.
-  TextDecoder always accept plain buffers as input.
+  TextDecoder always accepts plain buffers as input.

config/examples/low_memory.yaml

@@ -90,3 +90,4 @@ DUK_USE_COROUTINE_SUPPORT: false
 DUK_USE_SOURCE_NONBMP: false  # <300 bytes footprint
 DUK_USE_ES6_PROXY: false  # roughly 2kB footprint
 DUK_USE_ES7_EXP_OPERATOR: false  # pulls in pow()
+DUK_USE_ENCODING_BUILTINS: false