Remove unused variables

Since some variables with module LatinIME are defined but not used,
when compiled with build combination "sdk_pc_x86_64-userdebug" and
build command "mmm packages/inputmethods/LatinIME", the following
code lines will be reported that "variable 'XXX' set but not used".
(should be similar for all the other build combinations)

Repeated 10 times for each:
terminal_position_lookup_table.cpp:74:9 removedEntryCount
terminal_position_lookup_table.cpp:85:9 removedEntryCount
proximity_info_state_utils.cpp:493:9 tempTime
trie_map.cpp:56:9 unusedRegionSize
suggestion_results.cpp:100:9 index

Repeated 80+ times:
proximity_info_utils.h:75:25 proximityChar

With this patch we are removing some of the unused variables and
putting the C++ 17 attribute [[maybe_unused]] to the others which
are used for logging. Then all the related build warnings have been
eliminated.

Test: mmm packages/inputmethods/LatinIME, presubmit check.

Change-Id: Ia66766322d6ae8a010b1cb55cc22993fbc6d012c
Signed-off-by: Jing Mike <jingyangliu@eswincomputing.com>