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/esp32-s3-pico/platformio.ini

@@ -16,9 +16,9 @@ build_flags = ${esp32_base.build_flags}
   ;-DPRIVATE_HW
   -Ivariants/esp32-s3-pico
   -DBOARD_HAS_PSRAM
-  -DTECHO_DISPLAY_MODEL=GxEPD2_290_T94_V2
-  -DEPD_HEIGHT=128
-  -DEPD_WIDTH=296
+  -DEINK_DISPLAY_MODEL=GxEPD2_290_T94_V2
+  -DEINK_WIDTH=296
+  -DEINK_HEIGHT=128
 
 lib_deps = ${esp32s3_base.lib_deps}
   zinggjm/GxEPD2@^1.5.3