remove xpath useless method

[codeskyblue]

• add RPCStackOverflowError
• remove useless code, fix find_last_match

support new usage

(d.xpath("App") | d.xpath("NFC")).click()

(d.xpath("//android.widget.TextView") & d.xpath("App")).click()

[codecov]

Codecov Report

Attention: Patch coverage is 55.44041% with 86 lines in your changes are missing coverage. Please review.

Project coverage is 24.87%. Comparing base (64c6f2b) to head (32437ef).

Files	Patch %	Lines
uiautomator2/xpath.py	63.30%	42 Missing and 9 partials ⚠️
uiautomator2/core.py	20.00%	16 Missing ⚠️
uiautomator2/utils.py	8.33%	11 Missing ⚠️
uiautomator2/__init__.py	33.33%	4 Missing ⚠️
uiautomator2/watcher.py	60.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #976      +/-   ##
==========================================
+ Coverage   24.39%   24.87%   +0.47%     
==========================================
  Files          19       19              
  Lines        2820     2802      -18     
  Branches      430      429       -1     
==========================================
+ Hits          688      697       +9     
+ Misses       2106     2080      -26     
+ Partials       26       25       -1     

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