Don't use substitutions in tox.ini.

These seem to break things on Ubuntu Trusty...

tox.ini

@@ -26,8 +26,6 @@ deps =
     pytest-qt==1.4.0
     pytest-mock==0.6.0
     pytest-html==1.3.1
-# We don't use {[testenv:mkvenv]commands} here because that seems to be broken
-# on Ubuntu Trusty.
 commands =
     {envpython} scripts/link_pyqt.py --tox {envdir}
     {envpython} -m py.test --strict -rfEsw {posargs}
@@ -40,7 +38,7 @@ deps =
     pytest-cov==1.8.1
     cov-core==1.15.0
 commands =
-    {[testenv:mkvenv]commands}
+    {envpython} scripts/link_pyqt.py --tox {envdir}
     {envpython} -m py.test --strict -rfEswx -v --cov qutebrowser --cov-report term --cov-report html {posargs}
 
 [testenv:misc]
@@ -60,7 +58,7 @@ deps =
     logilab-common==0.63.2
     six==1.9.0
 commands =
-    {[testenv:mkvenv]commands}
+    {envpython} scripts/link_pyqt.py --tox {envdir}
     {envdir}/bin/pylint scripts qutebrowser --rcfile=.pylintrc --output-format=colorized --reports=no --expected-line-ending-format=LF
     {envpython} scripts/run_pylint_on_tests.py --rcfile=.pylintrc --output-format=colorized --reports=no --expected-line-ending-format=LF
 
@@ -84,7 +82,7 @@ deps =
     pyflakes==0.9.0
     pytest-flakes==1.0.0
 commands =
-    {[testenv:mkvenv]commands}
+    {envpython} scripts/link_pyqt.py --tox {envdir}
     {envpython} -m py.test -q --flakes -m flakes
 
 [testenv:pep8]
@@ -95,7 +93,7 @@ deps =
     pep8==1.6.2
     pytest-pep8==1.0.6
 commands =
-    {[testenv:mkvenv]commands}
+    {envpython} scripts/link_pyqt.py --tox {envdir}
     {envpython} -m py.test -q --pep8 -m pep8
 
 [testenv:mccabe]
@@ -106,7 +104,7 @@ deps =
     mccabe==0.3
     pytest-mccabe==0.1
 commands =
-    {[testenv:mkvenv]commands}
+    {envpython} scripts/link_pyqt.py --tox {envdir}
     {envpython} -m py.test -q --mccabe -m mccabe
 
 [testenv:pyroma]
@@ -115,7 +113,7 @@ deps =
     pyroma==1.8.1
     docutils==0.12
 commands =
-    {[testenv:mkvenv]commands}
+    {envpython} scripts/link_pyqt.py --tox {envdir}
     {envdir}/bin/pyroma .
 
 [testenv:check-manifest]
@@ -123,7 +121,7 @@ skip_install = true
 deps =
     check-manifest==0.25
 commands =
-    {[testenv:mkvenv]commands}
+    {envpython} scripts/link_pyqt.py --tox {envdir}
     {envdir}/bin/check-manifest --ignore 'qutebrowser/git-commit-id,qutebrowser/html/doc,qutebrowser/html/doc/*,*/__pycache__'
 
 [testenv:docs]
@@ -132,7 +130,7 @@ whitelist_externals = git
 deps =
     -r{toxinidir}/requirements.txt
 commands =
-    {[testenv:mkvenv]commands}
+    {envpython} scripts/link_pyqt.py --tox {envdir}
     {envpython} scripts/src2asciidoc.py
     git --no-pager diff --exit-code --stat
     {envpython} scripts/asciidoc2html.py {posargs}
@@ -143,8 +141,6 @@ setenv = QT_QPA_PLATFORM_PLUGIN_PATH={envdir}/Lib/site-packages/PyQt5/plugins/pl
 passenv = DISPLAY XAUTHORITY HOME USERNAME USER
 deps =
     -r{toxinidir}/requirements.txt
-# We don't use {[testenv:mkvenv]commands} here because that seems to be broken
-# on Ubuntu Trusty.
 commands =
     {envpython} scripts/link_pyqt.py --tox {envdir}
     {envpython} -m qutebrowser --no-err-windows --nowindow --temp-basedir about:blank ":later 500 quit"