feat(explore): replacing chart select with icons

[doralchan]

Before:

After:

Note: The Explore table will be the legend for multiple lines. Otherwise, a single line is already corresponds with the title (i.e. count is in the header so it doesn't need to be a legend item)

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

:white_check_mark: All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
static/app/views/explore/charts/index.tsx	0.00%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #78485      +/-   ##
==========================================
- Coverage   78.14%   78.13%   -0.01%     
==========================================
  Files        7099     7099              
  Lines      312893   312894       +1     
  Branches    51094    51095       +1     
==========================================
  Hits       244495   244495              
- Misses      62018    62019       +1     
  Partials     6380     6380