Remove ESCSERIAL from F7X2 targets

[haslinghuis]

Fixes #13220
Reverts #13078

According to comment in #12992 escserial does not work on F7 targets.

Think we need to remove USE_ESCSERIAL define from the F7 target for now.

[github-actions]

Do you want to test this code? You can flash it directly from Betaflight Configurator:

• Simply put #13221 (this pull request number) in the Select commit field of the Configurator firmware flasher tab (you need to Enable expert mode, Show release candidates and Development).

WARNING: It may be unstable. Use only for testing!

[blckmn]

AUTOMERGE: (FAIL)

• github identifies PR as mergeable -> FAIL
• assigned to a milestone -> PASS
• cooling off period lapsed -> PASS
• commit count less or equal to three -> PASS
• Don't merge label NOT found -> PASS
• at least one RN: label found -> PASS
• Tested label found -> FAIL
• assigned to an approver -> PASS
• approver count at least three -> FAIL

[Quick-Flash]

According to comment in #12992 escserial does not work on F7 targets.

Actually, according to that pull request it may work on F7 it is simply untested.

[McGiverGim]

What implies this? It's only used for passthrough for Kiss or it's needed to flash other ESCs like blheli32? To test it.

[SteveCEvans]

ESC_SERIAL works fine on the F7s. I use it myself where I'm using T-Motor ESCs with a BEC. I then power the FC from the BEC and need ESC-SERIAL to get the battery voltage.

We won't be removing it.