kconfig: Remove Wi-Fi on/off as a menuconfig option

kconfig: Remove Wi-Fi on/off as a menuconfig option

This is no longer required since the functions automatically get
pulled in based on the usage. A quick summary of footprint
comparisions before and after these set of patches is shown below:

Hello-World: (simplified for readability)
 old Total image size:~ 104902 bytes (.bin may be padded larger)
 old Total image size:~ 105254 bytes (.bin may be padded larger)
 Per-archive contributions to ELF file:
             Archive File DRAM .data & .bss   IRAM Flash code & rodata   Total
 old              libesp32.a       1973    177   4445       3939     2267   12801
 new              libesp32.a       1973    185   4473       3939     2267   12837

 new             libnvs_flash.a          0     92      0        274        8     374
 new             libstdc++.a          0      0      0         24        0      24

For some reason, nvs_flash.a (~400bytes) gets pulled in (particularly
the nvs_flash_init() function).

Power-Save: (simplified for readability)
 old Total image size:~ 421347 bytes (.bin may be padded larger)
 old Total image size:~ 421235 bytes (.bin may be padded larger)

 old      libtcpip_adapter.a          0     81      0       1947      115       2143
 new      libtcpip_adapter.a          0     69      0       1897      115       2081

The size actually shrinks a bit, since the AP interface function
doesn't get pulled in.