minadbd: Remove two warning options.

'-Wimplicit-function-declaration' is not needed (it's for C89) and
already enabled by -Wall.

For '-Wno-missing-field-initializers', don't see any existing case that
requires the flag.

Test: `mmma -j bootable/recovery` on aosp_{bullhead,marlin}-userdebug.
Change-Id: I46604723087ed9a7747f6cae31a95fc0074c6758