Refactor EInkDisplay (#3299)

* Refactor EInkDisplay
A lot of variant specific code is merged, with the macros pushed to the respective variant.h files.
"Dynamic Partial" code has been purged, pending a rewrite.

* fix: declare class only if USE_EINK, init all members

* refactor: move macros to platformio.ini
Responds to https://github.com/meshtastic/firmware/pull/3299#issuecomment-1966425926

* fix: EInkDisplay::connect() references old macros
Usage was in a block of variant-specific code, which had been intentionally left untouched.

* fix: remove duplicate macros from variant.h

---------

Co-authored-by: Ben Meadors <benmmeadors@gmail.com>

variants/heltec_wireless_paper/platformio.ini

@@ -2,7 +2,12 @@
 extends = esp32s3_base
 board = heltec_wifi_lora_32_V3
 build_flags = 
-  ${esp32s3_base.build_flags} -D HELTEC_WIRELESS_PAPER -I variants/heltec_wireless_paper
+  ${esp32s3_base.build_flags} 
+  -I variants/heltec_wireless_paper
+  -D HELTEC_WIRELESS_PAPER 
+  -D EINK_DISPLAY_MODEL=GxEPD2_213_FC1
+  -D EINK_WIDTH=250
+  -D EINK_HEIGHT=122
 lib_deps =
   ${esp32s3_base.lib_deps}
   https://github.com/ixt/GxEPD2#39f325b677713eb04dfcc83b8e402e77523fb8bf