[fix] webapp.py - running without installation is not supported

Remove extension of the sys.path (aka PYTHONPATH).  Running instance directly
from repository's folder is a relict from the early beginning in
2014 (fd651083f) and is no longer supported.

Since commit dd46629 was merged the command line 'searx-run' exists and should
be used.

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

docs/blog/python3.rst

@@ -25,19 +25,16 @@ How to run searx using Python 3
 Please make sure that you run at least Python 3.5.
 
 To run searx, first a Python3 virtualenv should be created.  After entering the
-virtualenv, dependencies must be installed. Then run searx with python3 instead
-of the usual python command.
+virtualenv, dependencies and searx must be installed. Then run searx from the
+command line.
 
 .. code:: sh
 
-    virtualenv -p python3 venv3
+    python3 -m venv venv3
     source venv3/bin/activate
-    pip3 install -r requirements.txt
-    python3 searx/webapp.py
-
-
-If you want to run searx using Python2.7, you don't have to do anything
-differently as before.
+    pip install -U pip setuptools wheel pyyaml
+    pip install -e .
+    searx-run
 
 Fun facts
 =========

searx/webapp.py

@@ -22,10 +22,6 @@ if sys.version_info[0] < 3:
     print('\033[1;31m Python2 is no longer supported\033[0m')
     exit(1)
 
-if __name__ == '__main__':
-    from os.path import realpath, dirname
-    sys.path.append(realpath(dirname(realpath(__file__)) + '/../'))
-
 # set Unix thread name
 try:
     import setproctitle